An introduction to physiological and systematical botany/Chapter 14
Gemma, a Bud, contains the rudiments of a plant, or of part of a plant, for a while in a latent state, till the time of the year and other circumstances favour their evolution. In the bud therefore the vital principle is dormant, and its excitability is accumulated. The closest analogy exists between buds and bulbs; and indeed the Dentaria bulbifera, Engl. Bot. t. 309, Lilium bulbiferum, Jacq. Fl. Austr. t. 226, and Gerarde emac. 193, with other similar plants, as mentioned p. 111, almost prove their identity.
Buds of trees or shrubs, destined for cold countries, are formed in the course of the summer in the bosoms of their leaves, and are generally solitary; but in the Blue-berried Honeysuckle, Lonicera cærulea, Jacq. Fl. Austr. append. t. 17 they grow one under another for three successive seasons. The buds of the Plane-tree, Platanus, Du Hamel Arb. v. 2. 171, are concealed in the footstalk, which must be removed before they can be seen, and which they force off by their increase; so that no plant can have more truly and necessarily deciduous leaves than the Plane. Shrubs in general have no buds, neither have the trees of hot climates. Linnæus once thought the presence of buds might distinguish a tree from a shrub, but he was soon convinced of there being no real limits between them.
The situation of buds is necessarily like that of the leaves, alternate, opposite, &c. Trees with opposite leaves have three buds, those with alternate ones a solitary bud, at the top of each branch. Du Hamel.
Buds are various in their forms, but very uniform in the same species or even genus. They consist of scales closely enveloping each other, and enfolding the embryo plant or branch. Externally they have often an additional guard, of gum, resin or woolliness, against wet and cold. The Horse Chesnut, Æsculus Hippocastanum, now so common with us, though, as I have learnt from Mr. Hawkins, a native of Mount Pinclus in Arcadia, is a fine example of large and well-formed buds; and some of the American Walnuts are still more remarkable.
It has been already remarked, p. 90, that buds resist cold only till they begin to grow: hence, according to the nature and earliness of their buds, plants differ in their powers of bearing a severe or variable climate.
Grew is elaborate on the forms of buds, and the arrangement of the spots apparent within them when cut transversely, which indicate the number and situation of their vessels. It was the character of this excellent man to observe every thing, without reference to any theory, and his book is a storehouse of facts relating to vegetation. Loefling, a favourite pupil of Linnaeus, wrote, under the eye of his great teacher, an essay on this subject, published in the Amænitates Academicæ, v. 2, in which the various forms of buds, and the different disposition of the leaves within them, are illustrated by numerous examples. The Abbé de Ramatuelle had taken up this subject with great zeal at Paris, about twenty years ago, but the result of his inquiries has not reached me.
Dr. Darwin, Phytologia, sect. 9, has many acute observations on the physiology of buds, but he appears to draw the analogy too closely between them and the embryo of a seed, or the chick in the egg. By buds indeed, as we well know, plants are propagated, and in that sense each bud is a separate being, or a young plant in itself; but such propagation is only the extension of an individual, and not a reproduction of the species as by seed. Accordingly, all plants increased by buds, cuttings, layers or roots, retain precisely the peculiar qualities of the individual to which they owe their origin. If those qualities differ from what are common to the species, sufficiently to constitute what is called a variety, that variety is perpetuated through all the progeny thus obtained. This fact is exemplified in a thousand instances, none more notorious than the different kinds of Apples, all which are varieties of the common Crab, Pyrus Malus, Engl. Bot. t. 179; and I cannot but assent to Mr. Knight's opinion, that each individual thus propagated has only a determinate existence, in some cases longer, in others shorter; from which cause many valuable varieties of apples and pears, known in former times, are now worn out, and others are dwindling away before our eyes. New varieties of Cape Geraniums, raised from seed in our greenhouses, are of still shorter duration, and can be preserved by cuttings for a few successive seasons only; yet several of these stand in our botanic works, with all the importance of real species. Gardeners know how many of the most hardy perennial herbs require to be frequently renewed from seed to exist in full vigour; and though others appear to our confined experience, unlimited in that respect, we have many reasons to believe they are not so. Propagation by seeds is therefore the only true reproduction of plants, by which each species remains distinct, and all variations are effaced; for though new varieties may arise among a great number of seedling plants, it does not appear that such varieties owe their peculiarities to any that may have existed in the parent plants. How propagation by seed is accomplished will be explained in a future chapter, as well as the causes of some varieties produced by that means.
Mr. Knight, in the Philosophical Transactions for 1805, has shown that buds originate from the alburnum, as might indeed be expected. The trunks and branches of trees, and the knobs of genuine tuberous roots, like the potatoe, are studded with them; in which respect, as Professor Willdenow judiciously observes, Principles of Botany, p. 15, such roots essentially differ from bulbous ones, which last are themselves simple buds, and produce their shoots, as well as their offsets, either from the centre or from the base.
The contents of buds are different, even in different species of the same genus, as Willows. The buds of some produce leaves only, others flowers; while in other species the same bud bears both leaves and flowers. Different causes, depending on the soil or situation, seem in one case to generate leaf-buds, in another flower-buds. Thus the Solandra grandiflora, Tr. of Linn. Soc. v. 6. 99. t. 6, a Jamaica shrub, was for a number of years cultivated in the English stoves, and propagated extensively by cuttings, each plant growing many feet in length every season, from abundance of moisture and nourishment, without showing any signs of fructification. At length a pot of the Solandra was accidentally left without water in the dry stove at Kew; and in consequence of this unintentional neglect, the luxuriant growth of its branches was greatly checked, and a flower came forth at the extremity of each. By a similar mode of treatment the same effect has since frequently been produced. Several plants, especially with bulbous roots, which blossom abundantly in their native soils, have hitherto defied all the art of our gardeners to produce this desirable effect; yet future experience may possibly place it within our reach by some very simple means. In general, whatever checks the luxuriant production of leaf-buds, favours the formation of flowers and seeds. That variety, or perhaps species, of the Orange Lily, Lilium bulbiferum, which is most prolific in buds, seldom forms seeds, or even those organs of the flower necessary to their perfection. So likewise the seeds of Mints, a tribe of plants which increase excessively by roots, have hardly been detected by any botanist; and it is asserted by Doody in Ray's Synopsis, that when the elegant little Ornithopus perpusillus, Engl. Bot. t. 369, does not produce pods, it propagates itself by the grains or tubercles of its root, though in general the root is annual.