An introduction to physiological and systematical botany/Chapter 19
OF THE FLOWER AND FRUIT.
Nothing can be more happy than the Linnæan definition of these organs; Phil. Bot. 52. "The fructification is a temporary part of vegetables, destined for the reproduction of the species, terminating the old individual and beginning the new."
Having examined the general structure and external form of plants, we now come to more important and even essential, though more transitory organs—the flower and fruit, or parts of fructification. By these each species is perpetually renewed without limits, so far at least as the observation of mankind has reached; while, as we have already mentioned, all other modes of propagation are but the extension of an individual, and sooner or later terminate in its total extinction.
Pliny had long ago beautifully said that "blossoms are the joy of trees, in bearing which they assume a new aspect, vyeing with each other in the luxuriance and variety of their colours." Linnæus has justly applied this to plants in general, and, improving upon the idea, he considers their herbage as only a mask or clothing, by no means indicative of their true nature or character, which can be learned from the flower and fruit alone.
Mr. Knight has traced his central vessels, by which the sap is conveyed from the root, into the flower and fruit. On the returning sap in the bark of these parts he has not been able to make any distinct observation; but he has determined that no matter of increase is furnished from the flowers or their stalks, as from leaves, to the part of the branch below them, nor indeed to any other part, Phil. Trans. for 1801, p. 340. There can be no doubt that certain parts of the flower, which we shall presently describe, perform functions respecting air and light analogous to those of leave, but entirely subservient to the benefit of the flower and fruit. Their secretions, formed from the returning sap, are confined to their own purposes. As soon as these are accomplished, a decided separation of vessels takes place, and the ripe fruit, accompanied perhaps by its stalk, falls from the tree. Dr. Hales tried in vain to give any flavour to fruit by the most penetrating and volatile fluids conveyed through the sap-vessels; for the laws of secretion are absolute in the organs of the flower, and their various results are, if possible, more strikingly distinct than even those we have contemplated in the leaves.
It is scarcely necessary to repeat that the fructification is essential to vegetables. A plant may be destitute of stem, leaves, or even roots, because, if one of these parts be wanting, the others may perform its functions, but it can never be destitute of those organs by which its species is propagated. Hence, though many individual plants may be long without blossoms, there are none, so far as nature has been thoroughly investigated, that are not capable, in favourable circumstances, of producing them, as well as seeds; to whose perfection the blossoms themselves are altogether subservient. Linnæus distinguishes seven parts of fructification, some of which are essential to the very nature of a flower or fruit, others not so indispensably necessary, and therefore not universal.
I. Calyx, the Calyx or Flower-cup, generally resembling the leaves in texture and colour, and forming the outermost part of a flower. This is not essential, and is often absent.
II. Corolla, the Corolla, or more delicate coloured internal leaf or leaves, properly petals, of a flower, likewise not essential.
III. Stamen, or Stamina, the Stamen or Stamens, commonly of a slender or threadlike form, bearing some kind of knob or cellular body, and ranged internally with respect to the Corolla. These are essential.
IV. Pistillum, or Pistilla, the Pistil, or Pistils, in the centre of the flower, consisting of the rudiments of the fruit, with one or more organs attached to them, and, of course, essential.
V. Pericarpium, the Seed-vessel, or a pulpy, woody, or leathery texture, enclosing the seeds, but wanting in many plants.
VI. Semen, the Seed, the perfecting of which is the sole end of all the other parts.
VII. Receptaculum, the Receptacle, basis or point of connection. This must necessarily be present in some form or other.
I. Calyx. The Flower-cup, or more correctly the external covering of the flower, when present, was originally divided by Linnæus into seven kinds, some of which are more justly so denominated than the others, and I have ventured to make an alteration in his list.
1. Perianthium. Calyx, properly and commonly so called, when it is contiguous to and makes a part of the flower, as the five green leaves which encompass a Rose, including their urn-shaped base; the two green bristly ones which enfold the bud in Glaucium luteum, Fl. Brit. Engl. Bot. t. 8; the tubular part, comprehending the scales at its base, in the Pinks, t. 61, 62, or the globular scale cup in Centaurea, t. 56. The Tulip, t. 63, is a naked flower, having no calyx at all.
This part is of an infinite variety of forms in different genera, being either simple or compound, divided or undivided, regular or irregular. In some instances it is permanent till the fruit is ripe, in others it falls even before the flower is well expanded.
2. Involucrum. Involucre of Professor Martyn; but I generally retain the Latin termination. This is remote from the flower, and can scarcely be distinguished from a Bractea. The term was first adopted by Linnæus, at the suggestion of his friend Artedi, in order to distinguish the genera of umbelliferous plants, for which purpose the latter deemed the part in question very important. But according to the laws which Linnæus had laid down, the parts of the flower and fruit alone were to afford generic characters, and the most sound botanists have ever since kept to this rule, with infinite advantage over less correct ones, however ready to derive ideas respecting the natural habit, and secondary characters, of a genus, not only from the inflorescence and bracteas, but even from the leaves, stipulas, or other parts. Linnæus and Artedi, therefore, were obliged to consider the involucra and involucella, the former accompanying the general and the latter the partial umbels, as a sort of calyx, and the umbel altogether as one aggregate flower, composed of florets united by a common radiated receptacle. Consequently a cyme must be considered in the same light; nor are reasons wanting in support of this hypothesis, which we shall consider after having first explained all the parts of fructification.
In Euphorbia, however, the term bractea would surely be more proper than involucrum or involucellum, as is evident from a consideration of the inflorescence of the whole genus, so very different in different species. In E. Peplis, and many others, the flowers are solitary and axillary; in others again, as E. amygdaloides, Engl. Bot. t. 256, and Characias, t. 442, some flower-stalks are umbellate, some scattered; and the subdivisions of the umbel in all are ultimately forked, that is, of a nature between umbellate and scattered. This genus has, moreover, a proper calyx or perianthium of a most distinct and peculiar nature. Some species of Anemone, a genus destitute of a perianthium, are said by Linnæus to have an involucrum, as A. Pulsatilla, t. 51, for which the name of bractea would be vastly more correct, though in A. Hepatica, Curt. Mag. t. 10, it is placed so near the flower as to seem a part of it, which, however, is really not the case.
The name of Involucrum is applied by Gleditsch to the membrane covering the fructification of ferns; nor have I, in studying this part with peculiar attention in order to reform the genera of these plants, see Tracts relating to Natural History p. 215, found reason to contrive any new appelation. My learned friends Willdenow and Swartz have judged otherwise, calling this membrane the indusium, or covering; which seems to me altogether superfluous. See its various forms in Engl. Bot. t. 1458–t. 60, t. 1150, t. 1159, t. 1160, &c.
3. Amentum. Catkin, denominated by authors before Linnæus julus, nucamentum, or catulus; consists of a common receptacle of a cylindrical form beset with numerous scales, each of which is accompanied by one or more stamens or pistils, so that the whole forms an aggregate flower. The receptacle itself and the bases of the scales are firmly united, and the whole catkin falls off entire, except that in some instances the upper part of each scale withers away, as in the Willow genus, Salix, Eng. Bot. t. 1388–90, 1402–4, &c., the seed-vessels in that genus being quite distinct from the scales. In others, the whole scale remains, enlarges, hardens, and protects the seed, as in Pinus, the Fir tribe. Such is the case with catkins of fertile flowers, which are necessarily permanent till the seed is ripe; barren ones fall as soon as the stamens have performed their office. Every catkin consists generally of either one kind of flower or the other. There are few certain and invariable instances of stamens and pistils in the same catkin, that circumstance occurring chiefly in a few species of Salix and Carex; nor is Typha, t. 1455–7, an exception to this. Examples of barren-flowered catkins are seen, not only in Salix and Pinus, but in several plants whose fertile or fruit-bearing flowers are not catkins, such as the Walnut, and, unless I am much mistaken, the Hasel-nut, t. 723. Each nut or seed of the latter has a permanent coriaceous calyx of its own, inadvertently called by Gærtner an involucrum, though he considers the whole as an amentum, which this very calyx proves it not to be. Humulus, the Hop, t. 427, has a catkin for the fertile flower only.
4. Spatha. Sheath, a covering which bursts longitudinally, and is more or less remote from the flower. This is exemplified in the Snow-drop, Galanthus nivalis, t. 167, the various species of Narcissus, t. 17, 275 and 276, and the Arum, t. 1298. The Spatha of the latter encloses a Spadix, or elongated receptacle, common to many flowers, according to the genuine Linnæan idea of this kind of calyx, taken from Palm-trees. In these the Spadix is branched.
6. Gluma. Husk, the peculiar calyx of Grasses and Grass-like plants, of a chaffy texture. These husks are usually compressed, embracing each other at the base, as in Phleum pratense, t. 1076. Sometimes they are depressed, flattened vertically, as in Briza, t. 540 and 1316. To the husk belongs the Arista, Beard or Awn, a bristle-shaped appendage, usually spiral, and possessing the property of an hygrometer. This, however, is not always present, even in different individuals of the same species.
"Unfortunately for the science,
On the awn there's no reliance."
The spiral kind of awn is most frequently attached to the Corolla of grasses, which is precisely of the same husky nature as their calyx, and is, by some botanists, considered as such. Specimens of glumæ muticæ, bearded husks, are seen in Phalaris canariensis, Engl. Bot. t. 1310, and glumæ aristatæ, awned ones, in Lagurus ovatus, t. 1334, and Stipa pennata, t. 1356.
6. Perichætium. A scaly sheath, investing the fertile flower, and consequently the base of the fruit-stalk, in some Mosses. In the genus Hypnum it is of great consequence, not only by its presence, constituting a part of the generic character, but by its differences in shape, proportion, and structure, serving frequently to discriminate species. See Engl. Bot. t. 1037—9, 1182, t. 1445—8, &c.; see also the same part in Neckera, t. 1443, 4. Linnæus apears by his manuscripts to have intended adding this to the different kinds of calyx, though it is not one of the seven enumerated in his printed works. Nor is he, surely, correct in allowing it to the genus Jungermannia. The membranous part which he there calls perichætium is strictly analogous indeed to the calyptra or veil of real mosses, esteemed by him a kind of calyx; but as I presume with Schreber to reckon it rather a corolla, and Hedwig once thought the same, and as Jungermannia has more or less of a real calyx besides, see Engl. Bot. t. 771, &c., I would no longer apply the term perichætium to this genus at all.
The part called calyptra being removed from the list, as being a corolla, the perichætium takes its place among the seven kinds of calyx. We lay less stress upon this coincidence than Linnæus might have done, when, according to the fashion of the times, he condescended to distribute his immortal Philosophia Botanica into 12 chapters and 365 sections, and reckoned seven parts of fructification as well as seven species of calyx.
7. Volva. Wrapper, or covering of the Fungus tribe, of a membranous texture, concealing their parts of fructification, and in due time bursting all round, forming a ring upon the stalk, as in Agaricus procerus, Sowerb. Fung. t. 190, and A. campestris, the Common Mushroom, t. 305.; Such at least is the original meaning of this term, as explained in the Phil. Bot; but it has become more generally used, even by Linnæus himself, for the more fleshy external covering of some other Fungi, which is scarcely raised out of the ground, and enfolds the whole plant when young. See Agaricus volvaceus, t. 1, and Lycoperdon fornicatum, t. 198; also the very curious L. phalloides, t. 390, now made a distinct genus by the learned Persoon, under the name of Batarrea phalloides.
Cæsalpinus the opinion that the Calyx proceeded from the bark, like the leaves, because of its similarity in colour and texture to those organs. He even refined upon the original idea, and supposed this part to proceed from the outer bark, while the more delicate corolla originated in the liber. What is now known of the physiology of the bark, as explained in several of our preceding chapters, renders this hypothesis totally inadmissible.Linnæus adopted from
The knowledge of the real use of leaves, see chapter 16, may however throw some light upon that of the calyx. Besides protection of the flower from external injuries, which is one evident use of this part, it appears highly probable that it may often contribute to the growth and strength of the stalk which supports it, as the leaves do to that portion of the branch below them. The stalk often swells considerably during the growth of the flower, especially just below the calyx, becoming more woody, an alteration frequently necessary for the support of the ripening fruit. When the calyx falls very early, as in the Poppy tribe, Papaver and Glaucium, I cannot find that the flower-stalk is subsequently enlarged, nor in any manner altered; while in genera without number, whose calyx is permanent, the stalk becomes not only more woody, but often considerably thickened.
II. Corolla. The Corolla, vulgarly called the leaves of the flower, consists of those more delicate and dilated, generally more coloured leaves, which are always internal with respect to the calyx, and constitute the chief beauty of a flower. In the Rose the Corolla is red and fragrant; in the Violet purple; in the Primrose yellow.
This term includes two parts, the Petal, Petalum, and the Nectary, Nectarium. The former is either simple, as in the Primrose, in which case the Corolla is said to be monopetalous, of one petal; or compound, as in the Rose, in which it is polypetalous, of several. The Nectary is sometimes a part of the petal, sometimes separate from it.
A monopetalous Corolla consists of two parts; the tube, tubus, the cylindrical part enclosed in the calyx of the Primrose; and the limb, limbus, which is the horizontal spreading portion of the same flower. The analogous parts of a polypetalous Corolla, as in the Wall-flower or Stock, are named the claw, unguis, and the border, lamina.
The Corolla is infinitely diversified in form in different genera, which Tournerfort and Rivinus derived their methods of arrangement. It is called regular when its general figure is uniform, as in the Rose, the Pink, the Columbine, Aquilegia vulgaris, Engl. Bot. t. 297, and Gentiana Pneumonanthe, t. 20; irregular when otherwise, as the Violet, t. 619, 620, Dead-nettle, t. 768, and Lathyrus, t. 805 and 1108. An equal Corolla is not only regular, but all its division are of one size, like those of the Primrose, t. 5, Campanula, t. 12, or Saxifraga, t. 9; an unequal one is when some segments are alternately smaller than the others, as in Butomus, t. 651, or otherwise different, as in Aquilegia, t. 297. It is by no means always necessary, in defining characters of genera, to use these last terms, it being sufficient in general to say that a Corolla is regular in opposition to one that is irregular; more especially as some species of a genus may possibly have an equal corolla, others an unequal one.
The most usual shapes of a monopetalous corolla are
campanulata, bell-shaped, as in Campanula, t. 12.
infundibuliformis, funnel-shaped, Pulmonaria, t. 118.
hypocrateriformis, salver-shaped, Primula, t. 4.
rotata, wheel-shaped, that is, salver-shaped with scarcely a tube, Borago, t. 36.
ringens, ringent, irregular and gaping like the mouth of an animal, Lamium, t. 768; called by former botanists labiata, lipped.
personata, personate, irregular and closed by a kind of palate, Antirrhinum, t. 129.
Those of a polypetalous one are
rosacea, rosaceous, spreading like a rose, Dryas, t. 451.
papilionacea, papilionaceous, irregular and spreading, somewhat like a butterfly, Lathyrus, t. 1108. The various petals which compose such a flower are distinguished by appropriate names, as vexillum, standard, the large one at the back; alœ, wings, the two side petals; and carina, the keel, consisting of two petals, united or separate, embracing the internal organs. In Trifolium all the petals are sometimes united into one at the lower part.
incompleta, incomplete, when parts, which analogy would lead us to expect, are deficient, as in Amorpha, a papilionaceous flower apparently, but consisting of the vexillum only; or Rittera of Schreber, a rosaceous one with a single lateral petal, seeming as if four others had been stripped off.
Linnæus was of opinion that the Corolla originated from the Liber or inner bark, as the Calyx from the outer, but this cannot be defended now the real physiology of the bark is better understood.
The whole use and physiology of the Corolla have not yet been fully explained. As a protection to the tender and important parts within, especially from wet, its use in many cases is obvious, but by no means in all. Linnæus imagined it to serve as wings, to waft the flower up and down in the air, and so to promote the functions of the Stamens and Pistils, as will hereafter by described; nor is this opinion unfounded.
Sprengel has ingeniously demonstrated, in some hundreds of instances, how the Corolla serves as an attraction to insects, indicating by various marks, sometimes perhaps by its scent, where they may find honey, and accommodating them with a convenient resting-place or shelter while they extract it. This elegant and ingenious theory receives confirmation from almost every flower we examine. Proud man is disposed to think that
because he has not deigned to explore it; but we find that even the beauties of the most sequestered wilderness are not made in vain. They have myriads of admirers, attracted by their charms, and rewarded with their treasures, which very treasures would be as useless as the gold of a miser to the plant itself, were they not thus the means of bringing insects about it. The services rendered by such visitants will be understood when we have described all the parts of a flower.
Besides the above purposes, I have always conceived the Corolla to fulfil some important office to the essential parts of the flower with respect to air, and especially light. It not only presents itself in a remarkable manner to the sun-beams, frequently closing or drooping when they are withdrawn, but it is so peculiarly distinguished by beauty or brilliancy of colour, that one cannot but think its functions somewhat different from those of the leaves, even with regard to light itself. Dr. Darwin calls the Corolla the lungs of the stamens and pistils, and with great probability, for they abound in air-vessels. But when we consider the elaborate and peculiar secretions of a flower, the elastic and inflammable pollen, the honey, and the exquisitely volatile perfume, as we know from the curious discoveries of modern chemistry how great a share light has in the production of such, we cannot but conclude that the petals must be of primary importance with respect to their secretion by its means.
Sometimes the Corolla is very short-lived; sometimes very lasting, even till the fruit is perfected, though mostly in a faded condition. In double flowers I have observed it to be much more durable than in single ones of the same species, as Anemones and Poppies, because, as I conceive, of its not having performed its natural functions, the stamens and pistils of such flowers being obliterated, or changed to petals; hence the vital principle of their corolla is not so soon exhausted as usual. Phil. Trans. for 1788, p. 165.
The Corolla, as already observed, is not essential. Whatever its functions may be, they can be occasionally performed by the Calyx perhaps, or even by the Filaments of the Stamens; as those of leaves are, in leafless plants, by the stems. When a flower has only one covering, it is not always easy to say whether that be a Calyx or Corolla. When green and coarse in texture like the former, we call it so, as in Chenopodium, Engl. Bot. t. 1033, and 1721—4, and the natural relationship of this genus to Polygonum, t. 1044, 989, 756, &c., leads us to reckon the same part in the latter a coloured calyx. On the other hand, when the part present is delicate and finely coloured, like the generality of Corollas, we denominate it such; more especially if the plant to which it belongs be allied to others that have a Calyx besides, as in Tulipa, t. 63, allied to Leucojum, t. 621, which has a Spatha. The great Jussieu denominates this part in the Tulip and other liliaceous plants, however beautiful, a Calyx. His definition of a Corolla is "that covering of a flower which is invested with the calyx, being very rarely naked; a continuation of the inner bark of the flower-stalk, not of its cuticle; not permanent, but mostly falling off with the stamens; surrounding or crowning the fruit, but never growing united with it; and having its parts of segments for the most part alternate with the stamens, which are equal to them in number." By this rule the tube and six segments of a Narcissus, t. 17, 275 and 276, constitute the Calyx, and then surely what Jussieu calls a Crown, and Linnæus a Nectary, must be allowed the name of Corolla. On the other hand, the Spatha becomes a Bractea. Consequently the whole order of Liliaceous flowers in general have a coloured Calyx only, which seems hardly admissible; and yet I cannot conceal a recent discovery which strongly confirms the opinion of my acute and candid friend. Two species of a new genus, found by Mr. Menzies on the West coast of North America, have beautiful liliaceous flowers like an Agapanthus, with six internal petals besides! I must however protest against the idea of the Corolla originating exclusively from the inner bark, as well as of the cuticle not being continued over it, for reasons sufficiently apparent from the former part of this work.
It is a Linnæan rule that the Stamens should be opposite to the segments of the Calyx, and alternate with the parts of the Corolla. Its author nevertheless seems of opinion that no absolute means of distinction between these two parts can be pointed out, except colour; of the insufficiency of which he is aware. If however the Corolla performs functions with respect to light which the Calyx does not, and those functions are indicated by its colour, a distinction founded on such a principle is both correct and philosophical. We must then conclude that in most liliaceous plants, not in all, the two organs are united into one, and indeed the outside is often green and coarse like a Calyx, the inner coloured and delicate; witness Ornithogalum, t. 21, 130 and 499, Narthecium, t. 535, &c. Linnæus has the same idea respecting Daphne, t. 119 and 1381, and the analogy is confirmed by Gnidia, which is a Daphne with petals. In Trollius, t. 28, and Helleborus, t. 200 and 613, Linnæus considers as petals what Jussieu, following Vaillant, thinks a Calyx. Of these plants we shall soon have occasion to speak again.
I cannot but consider as a sort of Corolla the Calyptra of Veil of Mosses, which Linnæus reckons a Calyx. Schreber, very deep and critical in his inquiries concerning these plants, and Hedwig, so famous for his discoveries among them, were both of this opinion, though the latter seems to have relinquished it. The organ in question is a membranous hood, covering the unripe fruit of these diminutive vegetables, like an extinguisher; but soon torn from its base, and elevated along with the ripening capsule. See Engl. Bot. t. 558, &c. The great peculiarity of this part, whatever it be called, consists in its summit performing the office of a stigma, as Hedwig first remarked. In Jungermannia, t. 771, &c., the very same part, differing only in usually bursting at the top to let the fruit pass, is named by Linnæus a perichætium, but very incorrectly, as we have already hinted.
Whatever office the Petals may perform with respect to air and light, it is probable that the oblong summit of the Spadix in Arum, t. 1298, answers the same purpose. When this part has been for a short time exposed to the light, it assumes a purplish brown hue, which M. Senebier seems to attribute to the same cause which he think produces the great heat observed in this flower, the rapid combination of oxygen gas with the carbon of the plant; an hypothesis hardly adequate to explain either.
Nectarium, the Nectary, may be defined as that part of the Corolla which contains or which secretes honey. It is perhaps in effect nearly universal, as hardly a flower can be found that has not more or less honey, though that liquor is far from being universally, or even generally, formed by any apparatus separate from the Petals. In monopetalous flowers, as Lamium album the Dead Nettle, t. 768, the tube of the corolla contains, and probably secretes, the honey, without any evident Nectary. Sometimes the part under consideration is a production or elongation of the Corolla, as in Violets; sometimes indeed of the Calyx, as in the Garden Nasturtium, Tropæolum, Curt. Mag. t. 23 and 98, whose coloured Calyx partakes much of the nature of the petals. Sometimes it is distinct from both, either resembling the petals, as in Aquilegia, Engl. Bot. t. 297, or more different, as in Epimedium, t. 438, Helleborus, t. 200 and 613, Aconitum, the Common Monkshood, and Delphinium, the Larkspur. Such at least is the mode in which Linnæus and his followers understand the four last-mentioned flowers; but we have already hinted that Jussieu is of a different opinion, and he even calls the decided Nectary of Epimedium an internal petal! Difficulties attend both theories. It seems paradoxical to call petals those singular bodies in Aconitum, like a pair of little birds, which are manifestly formed only to hold the honey, and not situated nor constructed so as to perform the proper functions of petals; but on the other hand Ranunculus, t. 100, 515 and 516, one of the same natural order, has evident calyx and petals, which latter have a honey-bearing pore in their claw, evincing their identity with the less petal-like Nectaries just described. Other instances indeed of Nectaries in the claws of petals are found in the Crown Imperial and Lily; which only confirms more strongly the compendious construction of the Lily tribe, the leaves of their flowers in these examples being Calyx, Petals and Nectaries all in one.
The most indubitable of all Nectaries, as actually secreting honey, are those of a glandular kind. In the natural order of Cruciform plants, composing the Linnæan class Tetradynamia, these are generally four green glands at the base of the Stamens. See Dentaria, Engl. Bot. t. 309, Sisymbrium, t. 525, and Brassica, t. 637. In Salix, t. 1488, and Geranium, t. 322, 75, &c., similar glands are observable; whilst in Pelargonium, the African Geranium, the Nectary is a tube running down one side of the flower-stalk.
The elegant Parnassia, t. 82, of which we are now acquainted with two new American species, has a most elaborate apparatus called by Linnæus Nectaries, but which the cautious Jussieu names Scales only. Linnæus usually called every supernumerary part of a flower Nectary, from analogy only, though he might not in every case be able to prove that such parts produced honey. This is convenient enough for botanical distinctions, though perhaps not always right in physiology; yet there is nothing for which he has been more severely and contemptuously censured. He was too wise to answer illiberal criticism, or he might have required his adversaries to prove that such parts were not Nectaries. Sometimes possibly he may seem to err, like L'Heritier, in calling abortive stamens by this name. Yet who knows that their filaments do not secret honey as wel as the tubes of numerous flowers? And though abortive as to Antheras, the Filament, continuing strong and vigorous, may do its office.
Honey is not absolutely confined to the flower. The glands on the footstalks of Passion-flowers yield it, and it exudes from the flower-stalks of some liliaceous plants.
The sweet viscis liquor in question has given rise to much diversity of opinion respecting its use. Pontedera thought it was absorbed by the seeds for their nourishment while forming, as the yolk of the egg by the chick. But Linnæus observes in reply, that barren flowers produce it as well as fertile ones, witness Urtica and Salix. In some instances the fertile flowers only are observed to bear honoey, as Phyllanthus and Tamus, but such cases are rare. Even Darwin says the honey is the food of the stamens and pistils, not recollecting that it is often lodged in spurs or cells quite out of the reach. There can be no doubt that the sole use of the honey with respect to the plant is to tempt insects, who in produring it fertilize the flower, by disturbing the dust of the Stamens, and even carry that substance from the barren to the fertile blossoms.
3. Stamina. The Stamens, formerly called Chives, are various in number in different flowers, from one to some hundreds. Their situation is internal with respect to the part we have been describing; external to the Pistils, at least in simple flowers.
These organs are essential, there being no plant hitherto discovered, after the most careful research, that is destitute of them, either in the same flower with the pistils, or a separate one of the same species.
A Stamen commonly consists of two parts, the Filament, Filamentum, and Anther, Anthera, the former being merely what supports the latter, which is the only essential part. Various forms and proportions of Filaments may be seen in the Tulip, where they are six in number, thick and short, Engl. Bot. t. 63; the Pink, where they are ten, much more slender, and answering to the idea of a filament or thread, t. 62; and Anenome, t. 51, where they are numerous. They are commonly smooth, but sometimes, as in Verbascum, t. 58, 59, bearded. In Melaleuca, Exot. Bot. t. 36 and 50, they are branched; and in Prunella, Engl. Bot. t. 961, forked, one point only bearing an Anther. In Aristolochia, t. 398, they are wanting, and nearly so in Potamogeton, t. 376, &c.
The Anther is the only essential part of a Stamen. it is generally of a membranous texture, consisting of two cells or cavities, bursting longitudinally at their outer edges, as in the Tulip. In Erica, t. 1013—15, it opens by pores near the summit, as in the Potatoε-blossom. Very rarely the Anther has four cells, as Tetratheca, Bot. of New Holl. t. 5, and Exot. Bot. t. 20—22. Sometimes it is ornamented with a crest, as in many Ericæ, and the genus Pinus. See Mr. Lambert's splendid work.
The Pollen, or Dust, is contained in the Anther, from which it is thrown out chiefly in warm dry weather, when the coat of the latter contracts and bursts. The Pollen, though to the naked eye a fine powder, and light enough to be wafted along by the air, is so curiously formed, and so various in different plants, as to be an interesting and popular object for the microscope. Each grain of it is commonly a membranous bag, round or angular, rough or smooth, which remains entire till it meets with any moisture, being contrary in this respect to the nature of the Anther; then it burst with great force, discharging a subtile vapour. In the Orchis family, and some other plants, the pollen is of a glutinous nature, very different from its usual aspect. See remarks on Mirabilis longiflora, Exot. Bot. v. 1. 44.
The stamens are changed to petals in double flowers, and rendered useless. They are often obliterated by excessive nourishment, or when the plant increases much by root, as in the Fiery Lily, or true Lilium bulbiferum.
4. Pistilla. The Pistils, no less essential than the Stamens, stand within them in the centre of the flower, and are generally fewer. When in a different flower, on the same or a different plant, that are not always central. Linnæus conceived them to originate from the pith, and the stamens from the wood, and hence constructed an ingenious hypothesis, relative to the propagation of vegetables, which is not destitute of observations and analogies to support it, but no countenanced by the anatomy and physiology of the parts alluded to.
Each Pistil consists of three parts. 1, the Germen, or rudiment of the young fruit or seed, which of course is essential; 2, the Stylus, style, various in length and thickness, sometimes altogether wanting, and when present serving merely to elevate the third part, Stigma. This last is indispensable. Its shape is various, either simple, scarcely more than a point, or capitate, forming a little round head, or variously lobed. Sometimes hollow, and gaping more especially when the flower is in its highest perfection; very generally downy, and always more or less moist with a peculiar viscid fluid, which in some plants is so copious as to form a large drop, though never big enough to fall to the ground. The moisture is designed for the reception of the pollen, which explodes on meeting with it; and hence the seeds are rendered capable of ripening, which, though in many plants fully formed, they would not otherwise be.
The Germen appears under a variety of shapes and sizes. It is of great moment for botanical distinctions to observe whether it be superior, that is, above the bases of the calyx and corolla, as in the Strawberry and Raspberry, or inferior, below them, as in the Apple and pear. Very rarely indeed the Germen is supposed by be betwixt the calyx and corolla, of which Sanguisorba, Engl. Bot. t. 1312, is reckoned by Linnæus an example; but the corolla there has really a tube, closely embracing the Germen. in Adoxa, t. 453, the calyx is half-inferior, the corolla superior. When in botanical language we say germen superior, it is equivalent to flower inferior; but it is sometimes more convenient and proper, for the sake of analogy or uniformity, to use one mode of expression than the other.
Pistils are sometimes obliterated, though oftener changed to petals, in double flowers, as well as the stamens; but I have met with a much more remarkable change in the Double Cherry, of the pistil into a real leaf, exactly conformable to the proper leaves of the tree, only smaller. By this we may trace a sort of round in the vegetable constitution. Beginning at the herbage or leaves, we proceed insensibly to bracteas in many species of Salvia, or to both calyx and corolla in the Garden Tulip, which frequently has a leaf half green half coloured, either in the flower or on the stalk just below it. Anemone alpina produces occasionally a petal among the segments of its involucrum or bractea. Geum rivale, Engl. Bot. t. 106, when cultivated in dry gravelly ground, exhibits such transformations in abundance. Between petals and stamens there is evidently more connection, as to their nature and functions, than between any other organs, and the commonly flourish and fall together. Yet only one instance is known of petals changing into stamens, which Dr. Withering has commemorated, in the Black Currant, Ribes nigrum. On the other hand, nothing is more frequent than the alteration of stamens to petals. Here then the metamorphosis begins to be retrograde, and it is still more so in the Cherry above mentioned, by which we return to the herbage again.—The line of distinction seems to be most absolute between stamens and pistils, which never change into each other; on the contrary, pistils, as we see, rather turn into petals, or even into leaves.
5. Pericarpium. The seed-vessel, extremely various in different plants, is formed of the germen enlarged. It is not an essential part, the seeds being frequently naked, and guarded only by the calyx, as in the first order of the Linnæan class Didynamia, of which Lamium, Engl. Bot. t. 768, and Galeopsis, t. 667, are examples; also in the great class of compound flowers, Syngenesia, as well as in Rumex, t. 724, Polygonum, t. 989, the Umbelliferous tribe, numerous Grasses, &c.
The use of the Seed-vessel is to protect the seeds till ripe, and then in some way or other to promote their dispersion, either scattering them by its elastic power, or serving for the food of animals in whose dung the seeds vegetate, or promoting the same end by various other mens. The same organ which remains closed so long as it is juicy or moist, splits and flies asunder when dry, thus scattering the seeds in weather most favourable for their success. By an extraordinary provision of Nature, however, in some annual species of Mesembryanthemum, natives of sandy deserts in Africa, the seed-vessel opens only in rainy weather; otherwise the seeds might, in that country, lie long exposed before they met with sufficient moisture to vegetate.
1. Capsula, a Capsule, is a dry seed-vessel of a woody, coriaceous or membranous texture, generally splitting into several valves; more rarely discharging its contents by orifices or pores, as in Campanula and Papaver; or falling off entire with the seed. Internally it consists either of one cell or several; in the latter case the parts which separate the cells are called dissepimenta, partitions. The central column to which the seeds are usually attached is named columella. See Datura Stramonium, Engl. Bot. t. 1288.
Gærtner, a writer of primary authority on fruits and seeds, reckons several peculiar kinds of Capsules, besides what are generally understood as such; these are
Utriculus, a Little Bladder, which varies in thickness, never opens by any valves, and falls off with the seed. I believe it never contains more than one seed, of which it is most commodiously, in botanical language, called an external coat, rather than a Capsule. Gærtner applies it to Chenopodium, as well as to Clematis, &c. In the former it seems a Pellicula, in the latter a Testa, as we shall hereafter explain.
Samara is indeed a species of Capsule, of a compressed form and dry coriaceous texture, with one or two cells, never bursting, but falling off entire, and dilated into a kind of wing at the summit or sides. It is seen in the Elm, the Maple, the Ash, Engl. Bot. t. 1692, and some other plants. This term however may well be dispensed with, especially as it is the name of a genus in Linnæus; an objection to which Cotyledon too is liable.
Folliculus, a Follicle or Bag, reckoned by Linnæus a separate kind of seed-vessel from the Capsule, ought perhaps rather to be esteemed a form of the latter, as Gærtner reckons it. This is of one valve and one cell, bursting lengthwise, and bearing the seeds on or near its edges, or on a receptacle parallel therewith. Instances are found in Vinca, t. 514, Pæonia, t. 1513, and Embothrium, Bot. of New Holland, t. 7—10. Coccum of Gærtner, separated by him from capsules, is a dry seed-vessel, more or less aggregate, not solitary, whose sides are elastic, projecting the seeds with great force, as in Euphorbia; also Boronia, Tracts on Nat. History, t. 4—7. This seems by no means necessary to be esteemed otherwise than a sort of capsule.
2. Siliqua, a Pod, is a long dry solitary seed-vessel of two valves, separated by a linear receptacle, along each of whose edges the seeds are ranged alternately, as in the class Tetradynamia. See Cheiranthus, Engl. Bot. t. 462, and Cardamine, t. 80; also Bignonia echinata, figured by Gærtner, t. 52, f. 1, which, though cautiously called by him a capsula siliquosa only, is as true a Siliqua, according to his own definition, and every body's ideas, as possible; so is also that of Chelidonium. He justly indeed names the fruit of Pæonia, capsula leguminosa, a follicle with him being a single-valved capsule, with the seeds marginal as in a legume.
Silicula, a Pouch, is only a Pod of a short or rounded figure, like Draba verna, Engl. Bot. t. 586. 3. Legumen, a Legume, is the peculiar solitary fruit of the Pea kind, formed of two oblong valves, without any longitudinal partition, and bearing the seeds along one of its margins only. See Engl. Bot. t. 1046, 805, &c. The Tamarind is a Legume filled with pulp, in which the seeds are lodged. The Capsules of Helleborus and some other plants allied thereto, justly indicated by Gærtner as approaching very nearly to the definition of Legumes, differ essentially in not being solitary, and in consisting each but of one valve. Some Larkspurs indeed bear such capsules solitary, but analogy teaches us their true nature.
When a Legume is divided into several cells, it is always by transverse constrictions, never by a separate longitudinal partition; see Dolichos purpureus, Exot. Bot. t. 74.Sometimes this kind of fruit lodges but one seed, as in many species of Trifolium; see Engl. Bot. t. 1048, also Viminaria denudata, Exot. Bot. t. 27. It is only by analogy that such are known to be Legumes.
4. Drupa, a Stone-fruit, has a fleshy coat, not separating into valves, containing a single hard and bony Nut, to which it is closely attached; as in the Peach, Plum, Cherry, &c.; see Engl. Bot. t. 706 and 1383. The Cocoa-nut is a Drupa with a less juicy coat.
Sometimes the Nut, though not separating into distinct valves, contains more than one cell, and consequently several seeds. Instances are found in Cornus, t. 249, Gærtner, t. 26, and Olea, the Olive, Fl. Græc. t. 3, though one cell of the latter is commonly abortive.
5. Pomum, an Apple, has a fleshy coat like the Drupa, but containing a Capsule with several seeds, as in common Apples and Pears; see Pyrus domestica, t. 350.
This is comprehended by Gærtner under the different kinds of Bacca, it being sometimes scarcely possible to draw the line between them; witness the Linnæan genus Sorbus.
6. Bacca, a Berry, is fleshy, without valves, containing one or more Seeds, enveloped with pulp. It becomes more juicy internally as it advances to maturity, quite contrary to the nature of a Capsule, though the difference between these two unripe fruits may not be discernible, and though some true Berries, when fully ripe, finally become of a dry and spongy texture; but they never open by valves or any regular orifice. Examples of a Bacca are seen in Atropa Belladonna, Engl. Bot. t. 592, and Ribes, t. 1289—92. The same part in Hedera, t. 1267, is of a more mealy substance. In Cucubalus, t. 1577, the coat only is pulpy. In Trientalis, t. 15, the coat becomes very dry and brittle as soon as ripe, and the cavity of the fruit is nearly filled by a globular columella. See Gærtner, t. 50.
Bacca composita, a Compound Berry, consists of several single ones, each containing a seed, united together, as in Rubus, the Raspberry, Bramble, &c., Engl. Bot. t. 715, 716, 826, 827. Each of the separate parts is denominated an Acinus, or Grain, which term Gærtner extends to the simple many-seeded berries of the Vine, Gooseberry, &c.
The Orange and Lemon are true Berries, with a thick coat. The Melon and Cucumber tribe have a peculiar sort of Berry for which Gærtner uses the name of Pepo, Gourd; and he defines it a Berry whose cells, together with the seeds, are remote from the axis or centre, the seeds being inserted into the sides of the fruit. Passiflora suberosa, Exot. Bot. t. 28, shows this insertion, being nearly allied to the same tribe; but in this genus the pulp invests each seed separately, forming Acini within the common cavity.
Some fruits ranged by Linnæus as Drupæ with many seeds, on account of the hardness of the shells of those seeds, are best perhaps, on account of their number, considered by Gærtner as Baccæ. Among these are Mespilus, the Medlar.
There are several spurious kinds of berries, whose pulp is not properly a part of the fruit, but originates from some other organ. Thus, in the Mulberry, as well as the Strawberry Spinach, Blitum, Curt. Mag. t. 276, the Calyx after flowering becomes coloured and very juicy, investing the seed, like a genuine berry. The Corolla of Commelina Zanonia undergoes a similar change, forming a black very juicy coat to the capsule, being totally altered both in shape and substance from its appearance in the flower. In the Juniper, Engl. Bot. t. 1100, a few scales of the fertile catkin become succulent, and coalesce into a globular berry with three or more seeds, to which Gærtner applies the term galbulus, the classical name of the Cypress fruit, which last however is as true a strobilus or cone as that of the Fir. In the Yew, t. 746, some have thought it a calyx, others a peculiar kind of receptacle, which becomes red and pulpy, embracing the seed. Lamarck has, in his Encyclopédie, v. 3. 228, considered this fruit as a real bacca or drupa, with the idea or definition of either of which it cannot by any means be made to accord, being open at the top, and having no connection with the stigma, which crowns the seed itself. The same writer mistakes for a calyx the scales, which analogy shows to be bracteas; and I cannot but think Jussieu and Gærtner more correct in their ideas of this singular fruit, when they call the pulpy part in question a receptacle, though the term calyx seems less paradoxical, and is perhaps still more just. We do not know enough of Taxus nucifera to draw any conclusions from thence. See Gærtner, t. 91. In the Strawberry, Engl. Bot. t. 1524, what is commonly called the berry is a pulpy receptacle, studded with naked seeds. In the Fig, Gærtner, t. 91, the whole fruit is a juicy calyx, or rather common receptacle, containing in its cavity innumerable florets, each of which has a proper calyx of its own, that becomes pulpy and invests the seed, as in its near relation the Mulberry. The Paper Mulberry of China is indeed an intermediate genus between the two, being as it were a Fig laid open, but without any pulp in the common receptacle.
7. Strobilus, a Cone, is a Catkin hardened and enlarged into a Seed-vessel, as in Pinus, the Fir.
In the most perfect examples of this kind of fruit the Seeds are closely sheltered by the scales as by a capsule, of which the Fir, Cypress, &c., are instances. In the Birch and Alder they have a kind of capsule besides, and in the Willow and Poplar a stalked bivalve capsule, still more separate from the scales. The Plane-tree, Platanus, the Liquidambar and the Comptonia, have globular catkins, in which bristles or tubercles supply the place of scales. See Gærtner, t. 90.
6. Semina. The Seeds are the sole "end and aim" of all the organs of fructification. Every other part is, in some manner, subservient to the forming, perfecting, or dispersing of these. A seed consists of several parts, some of which are more essential than others, and of these I shall speak first.
Embryo, the Embryo, or Germ, is the most essential of all, to which the rest are wholly subservient, and without which no seed is perfect, or capable of vegetation, however complete in external appearance. Linnæus, after Cæsalpinus, names it the Corculum, or Little Heart, and it is the point whence the life and organization of the future plant originate, as we have already explained, p. 96. In some seeds it is much more conspicuous than in others. The Walnut, the Bean, Pea, Lupine, &c., show the Embryo in perfection. Its internal structure, before it begins to vegetate, is observed by Gærtner to be remarkably simple, consisting of an uniform medullary substance, enclosed in its appropriate bark or skin. Vessels are formed as soon as the vital principle is excited to action, and parts are then developed which seemed not previously to exist, just as in the egg of a bird. In position, the Embryo is, with respect to the base of the whole flower or fruit, either erect, as in the Dandelion and other compound flowers, reversed as in the Umbelliferous tribe, or horizontal as in the Date Palm, Gærtner, t. 9. In situation it is most commonly within the substance of the seed, and either central as in Umbelliferous plants, or excentric, out of the centre, as in Coffee; in Grasses however it is external. Its direction is either straight, curved, or even spiral, in various instances. The Embryo of seeds that have a single cotyledon, or none at all, is peculiarly simple, without any notch or lobe, and is named by Gærtner Embryo monocotyledoneus.
Cotyledones, the Cotyledons or Seed-lobes, are immediately attached to the Embryo, of which they form, properly speaking, a part. They are commonly two in number; but in Pinus, and Dombeya, the Norfolk Island Pine, they are more, as already mentioned, p. 98. When the seed has sufficiently established its root, these generally rise out of the ground, and become a kind of leaves. Such is the true idea of the organs in question, but the same name is commonly given to the body of the seed in the Grass and Corn tribe, the Palms, and several other plants, thence denominated monocotyledones, because the supposed Cotyledon is single. The nature of this part we shall presently explain. It neither rises out of the ground, nor performs the proper functions of a Cotyledon, for what these plants produce is, from the first, a real leaf; or, if the plant has no leaves, the rudiment of a stem, as in Cuscuta. In either case, the part produced is solitary, never in pairs; hence Gærtner was led to reckon Cyamus Nelumbo, Exot. Bot. t. 31, 32, among the monocotyledonous plants, the body of its seed remaining in the earth, and the leaves springing one at a time from the Embryo, just as in the Date Palm, Wheat, Barley, &c.
The Seed-lobes of Mosses, according to the observations of Hedwig, Fund, part 2. t. 6; are above all others numerous and subdivided, as well as most distinct from the proper leaves; so that these plants are very improperly placed by authors among such as have no Cotyledons, a measure originating probably in theory and analogical reasoning rather than observation.Albumen, the White, is a farinaceous, fleshy, or horny substance, which makes up the chief bulk of some seeds, as Grasses, Corn, Palms, Lilies, never rising out of the ground nor assuming the office of leaves, being destined solely to nourish the germinating embryo, till its roots can perform their office. In the Date Palm, Gærtner, t. 9, this part is nearly as hard as a stone; in Mirabilis, Exot. Bot. t. 23, it is like wheat flour. It is wanting in several tribes of plants, as those with compound, or with cruciform flowers, and the Cucumber or Gourd kind, according to Gærtner. Some few leguminous plants have it, and a great number of others which, like them, have cotyledons besides. We are not however to suppose that so important an organ is altogether wanting, even in the abovementioned plants. The farinaceous matter, destined to nourish their embryos, is unquestionably lodged in their cotyledons, whose sweet taste as they begin to germinate often evinces its presence, and that it has undergone the same chemical change as in Barley. The Albumen of the Nutmeg is remarkable for its eroded variegated appearance, and aromatic quality; the cotyledons of this seed are very small.
t. 136, and Cyamus. In the natural order of Grasses the part under consideration forms a scale between the Embryo and the Albumen.Vitellus, the Yolk, first named and fully illustrated by Gærtner, is less general than any of the parts already mentioned. He characterizes it as very firmly and inseparably connected with the Embryo, yet never rising out of the integuments of the seed in germination, but absorbed, like the Albumen, for the nourishment of the Embryo. If the Albumen be present, the Vitellus is always situated between it and the Embryo, and yet is constantly distinct from the former. The Vitellus is esteemed by Gærtner to compose the bulk of the seed in Fuci, Mosses and Ferns, as well as in the genus Zamia, closely allied to the latter, see his t. 3, and even in Ruppia, Engl. Bot.
I cannot but think that the true use of the Vitellus may be to perform the functions of a Cotyledon with regard to air if not to light, till a real leaf can be sent forth, and that the "subterraneous Cotyledons" of Gærtner in the Horse Chesnut and Garden Nasturtium are, as he seems to indicate in his Introduction, p. 151, rather of the nature of a Vitellus. It does not appear that any plant with genuine ascending Cotyledons is likewise furnished with this organ; on the other hand, it commonly belongs to such as have the most copious Albumen, and therefore should seem to answer some other end than mere nutriment, which is supplied by the latter.
We learn from the above inquiries, that the old distinction between plants with one Cotyledon and those with several may still be relied on, though in the former the part which has commonly been so denominated is the Albumen, as in Corn, the real Cotyledon of which is the scale or Vitellus, which last organ however seems wanting in Palms, Lilies, &c., such having really no Cotyledon at all, nor any thing that can perform its office, except the stalk of their Embryo. In the Horse Chesnut, Oak and Walnut possibly, whose seed-lobes do not ascend, the functions of a real Cotyledon, as far as air is concerned, and those of the Albumen may be united in these lobes, as is the case with most Leguminous plants; which is rendered more probable, as several of the latter have the corresponding parts likewise remaining under ground. Hence the divided Vitellus of the Cyamus is to be considered as a pair of subterraneous Cotyledons, and the plant consequently ranges near its natural allies the Poppy tribe, as Mr. Salisbury, without the aid of physiology, has shown in the Annals of Botany, v. 2, p. 70, 75.
Testa, the Skin, contains all the parts of a seed above described, giving them their due shape; for the skin is perfectly formed, while they are but a homogeneous liquid. This coat differs in thickness and texture in different plants. It is sometimes single, but more frequently lined with a finer and very delicate film, called by Gærtner Membrana, as may be seen in a Walnut, and the kernel of a Peach, Almond, or Plum. Jn the Jasmine a quantity of pulp is lodged between the Membrana and the Testa, constituting a pulpy seed, semen baccatum, which is distinct from the Acinus, or grain of a compound berry in the Raspberry, the seed of the latter having its proper double covering within the pulp. The Testa bursts irregularly, and only from the swelling of its contents in germination.
Hilum, the Scar, is the point by which the seed is attached to its seed-vessel or receptacle, and through which alone life and nourishment are conveyed for the perfecting its internal parts. Consequently all those parts must be intimately connected with the inner surface of this scar, and they are all found to meet there, and to divide or divaricate from that point, more or less immediately. In describing the form or various external portions of any seed, the Hilum is always to be considered as the base. When the seed is quite ripe, the communication through this channel is interrupted: it separates from the parent plant without injury, a Scar being formed on each. Yet the Hilum is so far capable of resuming its former nature, that the juices of the earth are imbibed through it previous to germination.
There are various accessory parts, or appendages, to seeds, which come under the following denominations.
Pellicula, the Pellicle, called by Gærtner Epidermis, closely adheres to the outside of some seeds, so as to conceal the proper colour and surface of their skin, and is either membranous, and often downy, as in Convolvulus, or mucilaginous, not perceptible till the seed is moistened, as in Salvia verbenaca, Engl. Bot. t. 154. Perhaps the covering of the seed in Chenopodium, called by Gærtner Utriculus, is merely a Pellicula.
Arillus, the Tunic, is either a complete or partial covering of a seed, fixed to its base only, and more or less loosely or closely enveloping its other parts. Of this nature is the pulpy orange-coloured coat in Euonymus, t. 362, the beautiful scarlet cup in Afzelia, and the double membranous coat in Hippophäe, t. 425, which last invests the seed within the pulp of the berry. The outer of these coats only is described by Gærtner, as a peculiar membrane lining the cell of the berry; his "integumentum duplex" refers to the testa, which I mention only to prevent misapprehension. The Mace which envelopes the Nutmeg is a partial Arillus, beautifully drawn in Gærtner, t. 41. Narthecium, Engl. Bot. t. 535, has a complete membranous tunic, elongated beyond the seed at each end, as in many of the Orchis tribe; and such seeds, acquiring thence a light and chaffy appearance, have been denominated scorbiformia, whence Bergius was perhaps led, very unscientifically, to call the seeds of ferns literally scobs or sawdust! An elastic pouchlike Arillus, serving to project the seeds with considerable force, occurs in Oxalis, t. 762 and 1726. In the natural order of Rutaceæ the same part, shaped also like a pouch lining each cell of the capsule, is very rigid or horny; see Dictamnus albus, or Fraxinella, Gærtn. t. 69, and Boronia, Tracts on Nat. Hist. t. 4—7. Besides this coincidence, there are many common points of affinity between these plants and Oxalis, concerning colour, flavour, habit and structure. Fagonia and its allies form the connecting link between them, which Gærtner and Jussieu did not overlook. We have pointed out this affinity in English Botany, p. 762, and it is confirmed by the curious circumstance of Jacquin's Oxalis rostrata, Oxal. t. 22, having the very appendages to its filaments which make a peculiar part of the character of Boronia.
It is not easy to say whether the various, and frequently elaborate, coat of the seed among the rough-leaved plants, Borago, Anchusa, Lithospermum, Cynoglossum, Engl. Bot. t. 921, &c., should be esteemed an Arillus or a Testa, but the latter seems most correct, each seed having only a simple and very thin membranous internal skin besides. Gærtner therefore justly uses the term Nut for the seeds in question. The same may be observed of Ranunculus, Myosurus, see Engl. Bot. t. 435, Clematis, Anemone, &c., whose external coats are no less various and elaborate; yet such seeds are as truly naked as those of the Didynamia class, figured in Gærtner, t. 66, each having a double skin and no more, which is one covering less than even the genuine nut of the stone fruit, or of the Corylus. In Geranium, Malva, &c., what has often been called Arillus, is rather a kind of Capsule, not only because their seeds have a double or even triple skin, quite unconnected with this outer cover, but because the latter is analogous to other Capsules.
The loose husky covering of the seed in Carex is surely an Arillus. See Engl. Bot. also the Rev. Mr. Wood's observations on this genus in Dr. Rees's Cyclopædia, and Gærtner, v. 1. 13. This seed has besides a double Testa, though most of the true Grasses have but one, which in ground Corn constitutes the bran, the husks of the blossom being the chaff.
Pappus, the Seed-down, is restrained by Gærtner to the chaffy, feathery, or bristly crown of many seeds that have no Pericarpium, and which originates from a partial calyx crowning the summit of each of those seeds, and remaining after the flower is fallen. Instances of this are the feathery appendages to the seeds of Dandelion, Engl. Bot. t. 510, and Goat's-beard, t. 434, in which the part in question is elevated on a footstalk. In Carduus, t. 973—6, it is sessile, though still feathery; but in Cichorium, t. 539, it consists of mere chaffy teeth, more clearly evincing its affinity to a Calyx. In Scabiosa it is double. In Bidens, t. 1113, 1114, the Pappus is formed of 2, 3 or 4 rigid barbed bristles. The use of this organ is evidently to transport seeds to a distance from their native spot, either by resigning them to the power of the wind, or by attaching them to the shaggy coats of animals. In due time the feathery crown separates, and leaves the seed behind it, which happens sooner with the Thistle than most other plants. Hence the vacant down of that genus is frequently seen wafted in light masses over a whole country; which has not escaped the notice of poets.
The same term is used by the generality of botanists for the feathery crown of seeds furnished with a capsule, as Epilobium t. 1177, Asclepias, Cynanchum, &c., Gærtn. t. 117, as well as for a similar appendage to the base or sides of any seeds, as Salix, Engl. Bot. t. 183, 1403, Eriophorum, t. 873, &c., neither of which can originate from a Calyx. For the former of these Gærtner adopts the term Coma, for the latter Pubes, which last also serves for any downiness or wool about the Testa of a seed, as in the Cotton plant, and Blandfordia nobilis, Exot. Bot. t. 4.
Rostrum, a Beak, mostly applies to some elongation of a Seed-vessel, originating likewise from the permanent style, as in Geranium, t. 272, Helleborus, t. 200, though it is also used for naked seeds, as Scandix, t. 1397.
Ala, a Wing, is a dilated membranous appendage to Seeds, as in Embothrium, Bot. of N. Holl., t. 7, Banksia, Conchium, Bignonia echinata, Gærtn. t. 52, Rhinanthus, Engl. Bot. t. 657, serving to waft them along in the air. Gærtner wished to confine this term to a membranous expansion of the top or upper edge of a Seed or Seed-vessel, using margo membranaceus for one that surrounds the whole, but he has not adhered to it in practice. Capsules are sometimes furnished with one wing, as the Ash, oftener with several, as Halesia, Acer, Begonia, &c. In Seeds the Wing is commonly solitary, except some Umbelliferous plants, as Thapsia, Gærtn. t. 21.
Seeds are occasionally furnished with Spines, Hooks, Scales, Crested appendages, particularly a little gland-like part near the Scar, sometimes denominated Strophiolum, as in Asarum, Gærtn. t. 14, Bossiæa, Ventenat. Jard. de Cels. t. 7, Platylobium, Bot. of N. Holl. t. 6, Ulex, Spartium, &c. In general however smoothness is characteristic of a seed, by which it best makes its way into the soft earth, though sometimes it is barbed, or at least its covering, as in Stipa, Engl. Bot. t. 1356, that it may not easily be withdrawn again by the powerful feathery appendage of that plant, which after having by its circumvolutions forced the seed deeper and deeper, breaks off at a joint, and flies away.
The various modes by which seeds are dispersed cannot fail to strike an observing mind with admiration. Who has not listened in a calm and sunny day to the crackling of Furze bushes, caused by the explosion of their little elastic pods; nor watched the down of innumerable seeds floating on the summer breeze, till they are overtaken by a shower, which moistening their wings stops their further flight, and at the same time accomplishes its final purpose, by immediately promoting the germination of each seed in the moist earth? How little are children aware, as they blow away the seeds of Dandelion, or stick Burs in sport upon each other's clothes, that they are fulfilling one of the great ends of Nature! Sometimes the Calyx, beset with hooks, forms the bur, as in Arctium Lappa, Engl. Bot. t. 1228; sometimes hooks encompass the fruit itself, as in Xanthium, and some species of Galium, particularly G. Aparine, t. 816. Plants thus furnished are observed by Linnæus to thrive best in a rank manured soil, with which, by being conveyed to the dens of wild animals, they are most likely to meet. The Awns of grasses answer the same end. Pulpy fruits serve quadrupeds and birds as food, while their seeds, often small, hard and indigestible, pass uninjured through the intestines, and are deposited far from their original place of growth, in a condition peculiarly fit for vegetation. Even such seeds as are themselves eaten, like the various sorts of nuts, are hoarded up in the ground and occasionally forgotten, or carried to a distance, and in part only devoured. Even the ocean itself serves to waft the larger kinds from their native soil to far-distant shores.
The term Receptacle is sometimes extended by Linnaeus to express the base of a flower, or even its internal part between the stamens and pistils, provided there be any thing remarkable in such parts, without reference to the foundation of the whole fructification. It also expresses the part to which the seeds are attached in a seed-vessel.
7. Receptaculum. The Receptacle is the common base or point of connexion of the other parts of fructification. It is not ways distinguishable by any particular figure, except in compound flowers constituting the Linnæan class Syngenesia, in which it is very remarkable and important. In the Daisy, Engl. Bot. t. 424, it is conical; in Chrysanthemum, t. 601, convex; in others flat, or slightly concave. Picris, t. 972, has it naked, that is, destitute of any hairs or scales between the florets or seeds; Carduus, t. 675, hairy; Anthemis, t. 602, scaly; and Onopordum, t. 977, cellular like a honey-comb. On this and the seed-down are founded the most solid generic characters of these plants, admirably illustrated by the inimitable Gærtner.
Having thus explained the various organs of fructification, we shall add a few remarks concerning flowers in general, reserving the functions of the Stamens and Pistils, with the Linnæan experiments and inquiries relative to that curious subject, for the next chapter.
A flower furnished with both calyx and corolla is called flos completus, a complete flower; when the latter is wanting, incompletus; and when the corolla is present without the calyx, nudus, naked. When the stamens and pistils are both, as usual, in one flower, that flower is called perfect, or united; when they are situated in different flowers of the same species, such I would call separated flowers; that which has the stamens being named the barren flower, as producing no fruit in itself, and that with pistils the fertile one, as bearing the seed. If this separation extends no further than to different situations on the same individual plant, Linnæus calls such flowers monoici, monœcious, as confined to one house or dwelling; if the barren and fertile flowers grow from two separate roots, they are said to be dioici, diœcious. Some plants have united flowers and separated ones in the same species, either from one, two or three roots, and such are called polygamous, as making a sort of compound household.
A Compound flower consists of numerous florets, flosculi, all sessile on a common undivided Receptacle, and enclosed in one contiguous Calyx or Perianthium. It is also essential to this kind of flower that the Anthers should be united into a cylinder, to which only the genus Tussilago affords one or two exceptions, and Kuhnia another; and moreover, that the Stamens should be 5 to each floret, Sigesbeckia flosculosa of L'Heritier, Stirp. Nov. t. 19, alone having but 3. The florets are always monopetalous and superior, each standing on a solitary naked seed, or at least the rudiments of one, though not always perfected. Some Compound flowers consist of very few florets, as Humea elegans, Exot. Bot. t. 1, Prenanthes muralis, Engl. Bot. t. 457; others of many, as the Thistle, Daisy, Sunflower, c. The florets themselves are of two kinds, ligulati, ligulate, shaped like a strap or ribband, with 3 or 5 teeth, as in Tragopogon, t. 434, and the Dandelion; or tubulosi, tubular, cylindrical and 5-cleft, as in Carduus, t. 107, and Tanacetum, t. 1229. The marginal white florets of the Daisy are of the former description, and compose its radius, or rays, and its yellow central ones come under the latter denomination, constituting its discus, or disk. The disk of such flowers is most frequently yellow, the rays yellow, white, red, or blue. No instance is known of yellow rays with a white, red, or blue disk.
An Aggregate flower has a common undivided Receptacle, the Anthers all separate and distant, Jasione only, Engl. Bot. t. 882, having them united at the base, but not into a cylinder, and the florets commonly stand on stalks, each having a single or double partial calyx. Such flowers have rarely any inclination to yellow, but are blue, purple, or white. Instances are found in Scabiosa, t. 659 and 1311, Dipsacus, t. 1032 and 877, and the beautiful Cape genus Protea.
Such is the true idea of an Aggregate flower, but Linnæus enumerates, under that denomination, 7 kinds, his favourite number; these are,
1. The Aggregate flower properly so called, as just mentioned.
2. The Compound flower previously described.
3. The Amentaceous flower, or Catkin, of which we have spoken p. 248.
4. The Glumose, or Chaffy flower, peculiar to the Grasses, see p. 250.
5. The Sheathed flower, whose common receptacle springs from a Sheath, as in Arum.
6. The Umbellate; and
7. The Cymose flowers, concerning which two last a few observations are necessary.
Linnæus and his friend Artedi thought the great natural umbelliferous order could not be divided into good and distinct genera by the seeds or parts of the flower, without taking into consideration the general and partial involucral leaves, which they therefore chose to consider as a part of the fructification, and defined as a calyx remote from the flower. The rays of the umbel, of course, became the subdivisions of a branched receptacle, and the whole umbel was considered as one aggregate flower. It necessarily followed that a Cyme, see p. 237, must be considered in the same light, nor did the sagacity of Linnæus overlook the arguments in favour of this hypothesis. Many of the umbelliferous tribe, as Heracleum, t. 939, Caucalis, Coriandrum, &c., have their marginal flowers dilated, radiant, and more or less inclined to be imperfect or abortive, thus evincing an analogy with real compound flowers like the Sunflower, which analogy is still more striking between Oenanthe, t. 363, 347, 348, and the Marigold, Calendula. So the cymose plants, as Viburnum Opulus, t. 332, bear dilated and abortive marginal flowers, and Hydrangea hortensis, Sm. Ic. Pict. t. 12, has scarcely any others. Cornus sanguinea, Engl. Bot, t. 249, has a naked cyme, C. Suecica, t. 310, an umbel accompanied by coloured bracteas, or, as Linnæus judged, a coloured involucrum, proving the close affinity between these two modes of inflorescence.
Notwithstanding all this, I presume to dissent from the above hypothesis, as offering too great violence to Nature, and swerving from that beautiful and philosophical Linnæan principle, of characterizing genera by the fructification alone; a principle which, those who are competent to the subject at all, will, I believe, never find to fail. The seeds and flowers of the umbelliferous family are quite sufficient for our purpose, while the involucrum is very precarious and changeable; often deficient, often immoderately luxuriant, in the same genus. In the cymose plants every body knows the real parts of fructification to be abundantly adequate, the involucrum being of small moment; witness that most natural genus Cornus. For all these, and other reasons, to particularize which would lead me too far, I have, p. 236, reckoned the Umbel and Cyme modes of flowering, and not themselves aggregate flowers.
- It appears moreover that Carpinus, the Hornbeam, has hitherto erroneously been supposed to have an amentum for the fertile flower. The true nature of the covering of the seed, as well as of the common stalk, proves it otherwise.
- I submit to the opinion of Professor Martyn in adopting this word, for the reasons given in his Language of Botany, more especially as general practice seems to favour its use.
- In this plate the engraver has by mistake expressed the section of the anther so as to look more like a germen, though the original drawing was correct.
- Hernandia, Gærtn. t. 40, has a similar, though not succulent, calyx, and the green cup of the Hazlenut is equivalent to it.
- This may answer the purpose of a Cotyledon, just as the stems of many plants fulfil the office of leaves.