Evolution of Life/Botany
Botany.
While plants, in their external appearance, present every variety of size, shape, and color, their internal structure does not offer the same amount of difference as is observed in the divisions of the animal kingdom. The old dogma that plants live, but animals live and feel, still holds true; there not having been found in the vegetal kingdom a trace of a nervous system. Some other basis for the classification of plants must therefore be chosen. More than a century ago, Linnaeus divided the vegetal kingdom into Cryptogamia and Phanerogamia, which may, for the present, be translated Flowerless and Flowering plants. Modern science has offered nothing better than the classification of Linnaeus, it being a natural one. The Flowerless plants, or the Cryptogamia, include: 1st, the Algae, or the greenish matter covering bricks, stones, etc., the green thread-plants of ponds and ditches, and the red and black sea-weed; 2d, the Fungi, or toadstools, mushrooms, etc.; 3d, the Lichens, or the parchment-like growths seen covering fence-rails, etc.; 4th, the Mosses; 5th, the Ferns. The Flowering plants, or Phanerogamia, are represented by: 1st, the Cycadae, bread ferns, etc.; 2d, the Coniferae, pine, cypress; 3d, the Monocotyledons (one-seed lobe), lily, banana, palm; 4th, the Dicotyledons (two-seed lobes), elms, mulberry, geranium, rose. The first three classes of the Cryptogamia differ from the Phanerogamia in the absence of flowers,
and in wanting roots, stem, and leaves; the Mosses and 
Ferns, while cryptogamic I'n their flowerless condition, agree with the Phanerogamia in having stems and leaves; they are therefore intermediate in their structure; the transition forms leading from the simple water-plants, mushrooms, etc., to the pines and oaks.
ALGAE.
No class of plants is more interesting than the Algae. Notwithstanding their very simple structure, they offer every variety of shape, size, and color. While many of them are very minute, the beauty of their form, the delicacy of their structure, and their exquisite coloring, never have failed to attract the attention of the microscopist. The Confervoidae, or green Algae, are widely distributed, every pond, ditch, spring, and stream having representatives. The greenish matter seen on old trees, that found in bogs, the slime on stories in ponds, the silk-like threads of troughs, the sea-weed usually seen in marine aquaria, as well as innumerable other examples which might be given, serve to illustrate the green Algae, or Confervoidae. Among the green Algae we find the simplest and smallest of plants, the Chlorococcus viridis (Fig. 87), which, when aggregated in hundreds of millions, composes the greenish matter clothing in layers old trees, wood palings, etc. The Chlorococcus is a simple cell filled with granular contents. Under favorable circumstances each cell divides into halves (Fig. 88), each half becoming a new individual; this process may be continued indefinitely: such is the simple manner of reproduction in this very minute plant. Among the unicellular green Alga; are included the Desmidiaceae, which are found most often in open situations, as in the pools of bogs and moors. They are among the most beautiful of microscopic objects. Their most characteristic feature is that of bilateral symmetry, giving the impression that their body is composed of two cells, as seen in Euastrum, Cosmarium, Closterium (Figs. 89, 90, 92), or of many cells, as in Hyalotheca (Fig. 91), but they are really one-celled plants, as proved by the fact of all the green contents escaping if the cell-wall be broken, the indentations and constrictions being only superficial. The constriction of Cosmarium indicates the place where the body will divide into two halves, each half becoming a new individual. In some forms, as Pediastrum (Fig. 97), the green contents of the cell are transformed into ciliated bodies, or zoospores, which escape, the cell-wall breaking, and move about for some time (Fig. 98), then settle, coalesce, and finally take on the appearance of the parent plant. The green, thread-like plant of horse-troughs, etc. is generally composed of the Alga known as Spirogyra (Fig. 93). Each Spirogyra is a chain of cells, the green matter of the cells being disposed in the form of a spiral. At certain seasons of the year, adjacent Spirogyrae are seen to push out the walls of their cells towards each other until a communication is formed. (Fig. 94.) The green contents of one individual, leaving its cell, pass through the communicating process, and mix with the contents of its neighbor: this is later the beginning of a future Spirogyra. This kind of reproduction is known as conjugation, and is the simplest type of sexual reproduction, i.e., the union of two distinct germinal masses to form a spore. The Nostochaceae (Fig. 95) attached to stones are composed of a row of cells or beads, making filaments imbedded in a gelatinous kind of matter which is inclosed by a membrane; the membrane breaking, the gelatinous matter escapes into the water, carrying the filaments with it. The Nostochaceae have been considered by some botanists as an undeveloped form of Lichen. With the exception of the Ulvaceae (Fig. 96), which are marine in their habitat, the green Algae are confined to fresh water. The Ulva, from which the group takes 'its name, is the green plant which usually adorns marine aquaria. It is composed of layers of cells bound together, and its reproduction is effected by zoospores, such as we noticed in Pediastrum.
FUCOIDAE
The brown or olive-colored Algae, or Fucoidae, differ not only in their color from the green Algae, of which we have just spoken, but equally as regards their size and manner of reproduction. They are confined to the sea, and are found generally on submarine rocks, which are exposed, however, at low tide, to heat, light, and atmospheric influences. This seems to be necessary for the healthy growth of the brown Algae, since the specimens that are brought up from greater depths do not exhibit so hardy a structure as those that live at the surface. The Fucoidae are commonly known as sea-wrack; but that generally picked up at the sea-shore gives no idea of the immense size which some of the brown Algae attain, the Macrocystis of the Californian coasts reaching a length of four hundred feet. Among the Fucoidae are included the Laminaria, or leathery sea-weed; the Fucus (Fig. 99), or bladder-wrack, so called from floating on the surface of the sea by means of air-bladders. This bladder-like arrangement in the Sargassum, or gulf-weed, takes the form of a bunch of berries, and is the most characteristic feature of the plant. The importance of the brown Algae may be estimated from the fact that forty thousand square miles of the Atlantic Ocean are covered with a kind of oceanic forest of Sargassum. (Fig. 100.) The presence of this plant gave Columbus vain hopes of being near land. The reproduction of the brown Algae has not as yet been perfectly made out. It is known, however, that the process is sometimes carried on by zoospores, as in Pediastrum, or by the intervention of distinct germinal masses, which unite whilst free in the welter, to form a spore, a process corresponding to the so-called conjugation of the Spirogyra.
FLORIDAE.
The red or rose-colored Algae, though much smaller than the Fucoidae, surpass them greatly in beauty of coloring and delicacy of form. They are commonly known as red sea-weed, and, when dried and arranged on paper, they are often offered for sale. The Floridae (Fig. 101), or Red Algae, are from six inches to two feet high, offering in their coloring different shades of red, rose-red, and purple. Their form varies from that of a filament or stalk to that of a leaf or feather. To see them in perfection, they must be studied in a tropical climate. The reproduction of the Floridae is still involved in some mystery. There are in many species tetraspores (Fig. 102), which are formed by the division of the so-called perispore into four spores, which appear to correspond with the zoospores of the lower Algae. Besides these tetraspores, other reproductive bodies arise in some species from the union of two germs, which may be looked upon as the representatives of distinct sexes. While the Green, Brown, and Red Algae differ greatly in their size, form, coloring, and reproduction, they all agree in their cellular structure. When we compare a single individual of the Chlorococcus—so minute that hundreds of thousands might rest on the head of a knitting-needle—with the gigantic Macrocystis, notwithstanding minor differences, we find the essentially cellular structure of both to be the same. The group of Algae is, therefore, a natural one, the extremes being connected by innumerable links, offering a gradual transition from microscopic forms to the largest of plants. In the preceding chapter we have given reasons for supposing it probable that Monera in past time divided into animal and vegetal Monera, and endeavored to show how the animal kingdom may have descended from animal Monera. Although the precise time and exact manner in which the vegetal kingdom appeared may never, perhaps, from the nature of the case, be demonstrated, still, Prof. Haeckel's view of vegetal Monera having been the remote ancestors of the vegetal kingdom has so much in its favor that it may be accepted as a near approximation to the truth. Following, then, Prof. Haeckel, the vegetal Monera must be regarded as the ancestors of the Protophyta, or primitive plants, those most simple, unicellular Algae, like the Chlorococcus, etc., while the Green, Brown, and Red Algae represent the three diverging branches of a stem whose roots originate in the Protophyta.
FUNGI.
Mushrooms, puff-balls, smuts, mildews, truffles, moulds, although offering in minor points variety of structure, still agree in so many important respects, and differ so essentially from all other plants, that they are always associated by naturalists, and are regarded as forming the very natural group of Fungi. One of the most general laws of Biology is that while animals derive their nutriment solely from the organic world, plants, on the contrary, are nourished by inorganic matter; in other words, while plants by their life-processes change inorganic into organic matter, animals by their life-processes reconvert organic into inorganic matter. Fungi, in feeding solely on organic matter, agree with animals, and differ from all other plants. Amylum, or starch-flour, is one of the most constant products of the vegetal kingdom, yet no trace of this important principle is found among the Fungi. The green color so characteristic of plants, due to the presence of chlorophyll, is never seen in any Fungi. With some exceptions, the Fungi nourish themselves on organic matter, whereas plants combine inorganic matter, such as water, carbonic acid, ammonia, phosphates, etc., assimilating these principles in their growth. The life-processes, the absence of amylum and chlorophyll, are such important facts in the economy of the Fungi that some naturalists deny that they are plants at all, and wish to place them in the intermediate kingdom referred to in the preceding chapter. The reproduction of the Fungi, and the many transitional forms hardly distinguishable from Algae and Lichens, influence most botanists in regarding them as very aberrant, but still members of the vegetal kingdom.
Most Fungi are parasitic in their mode of existence, living at the expense of the plant or animal on which they are found.
The disease known as scald-head is due to the presence of a fungus, the Achorion; the thrush, a throat trouble, is caused by a fungus, the Oidium. Quite a flora has been described by Leidy and Robin as existing in the intestines of different animals, consisting principally of Fungi. The Fungi are found, however, in the greatest profusion on decaying vegetal matter, stumps of trees, etc. being converted into powder by them. When half-eaten fruit is allowed to stand, soon it is seen to be covered with a whitish film, which, when examined under the microscope, is found to be made up of the filaments of a Fungus. A Fungus, while essentially cellular, consists of two parts, the mycelium, or threads, and the colorless spores, or fruit: the threads are elongated cells, and resemble in position the stems of higher plants; the spores are seen at the end of the threads. (See Fig. 103, Grape Fungus.) The spores are sometimes free (stylospores), or they are inclosed in what is called an ascus. (See figure of Stilbospora and
Sphaeria, Fig. 104, b, c.) The arrangement of the spores 
or fruit, and the proportion of the size of the fruit to the mycelum or threads, have served as the basis of a classification of the Fungi. The mushroom, the puff-ball, the smut, the mildew, the truffle, and mould, are familiar examples of the different orders of Fungi. This classification, like all similar attempts, suffices, so long as types so different as a mushroom and mildew are compared. What are commonly collected as mushrooms are only the fruit of the fungus Agaricus: the greater part of the mildew examined show only the mycelium or threads of the fungus Botrytis. The mushrooms belong to the order Hymenomycetes, so called from the hymenium. Or part supporting the fruit, being so prominent, the threads being inconspicuous. The mildew (Fig. 105) illustrates the Hyphomycetes, which derive their name from the Hyphi, or threads, being so much developed, the fruit dropping off
The difficulty of classification arises from the fact that from time to time individuals are discovered which do not present such striking contrasts as the mushroom and mildew, their characters being so little defined as to make it impossible to say to what groups they belong. All such intermediate forms, the source of so much trouble in the arrangement of an herbarium, are most important proofs of the truth of the theory of the gradual transformation of plants. Not only is it true that, in the Fungi the orders pass insensibly into each other, but there are also forms of which it is doubtful whether they are Fungi, some botanists still regarding them rather as Algae. Thus, the Peronospora (Fig. 106), differing from Botrytis (mildew) in its continuous cells, the partitions of Botrytis (Fig. 105) being absent, is, according to Prof. Haeckel, a transitional form which links the Algse through Vaucheria (Fig. 107) with the Fungi, though the Peronospora is usually regarded as a Fungus, it having no chlorophyll. The Achlya, sometimes called Saprolegnia, formerly considered an Alga, seems to be only an aquatic form of the Sporendonema, the common fly fungus. It was long ago observed by Carus that the portions of a salamander which were above the surface of the water produced a Mucor (fungus), while those immersed gave rise to an Achlya (alga). While the Algae pass very gradually into the Fungi through intermediate forms like Vaucheria, Peronospora, Achlya, and Sporendonema, the transition from the Fungi to the Lichens is equally easy.
LICHENS.
Lichens are dry plants, covering stones and rocks, or creeping over trees, walls, and fences. They are found as gray, brown, yellow patches; as wrinkled, leathery, horny crusts (Fig. 108); and however unattractive, as a general rule, in appearance, are of great importance in the economy of nature, and therefore of interest to the botanist. The Lichens are widely distributed, being found in the icy recesses of Mont Blanc, amidst the recently poured-out lava of Vesuvius, and crowning the summits of most barren rocks. The Lichens, being aerial in habit, and more insensible to changes in climate than any other plants, survive and flourish where all other vegetation would perish. The decaying parts of their bodies furnish the subsoil in which future mosses, ferns, and flowering plants can take root. Their importance, therefore, cannot be over-estimated. A Lichen (Fig. 109) is made of threads, and colorless and green spores. The threads resemble the mycelium, or threads of a Fungus; the green spores (gonidia) are like the spores of the Algae (the spores of Fungi, being colorless, resemble the other spores). Most Lichens derive their nourishment from the air. This peculiarity is usually regarded as distinguishing them from Fungi, which live parasitically on plants and animals. But as certain forms of Fungi (according to Berkeley) are found on iron, lead, etc., certainly not living at the expense of these metals, the distinction of the aerial nutrition of Lichens from the parasitical of Fungi evidently does not hold good in all cases. The presence of green spores is very constant, but their absence in forms like Alrothallus makes Lichens of this kind undistinguishable from Fungi. Lichens, as a rule, are aerial plants; yet some forms are always immersed in water, as in most Algae. The early stages of many Lichens resemble so closely certain Algae that botanists cannot separate them. The Lichens are considered by most naturalists as standing between the Algae and Fungi. According to Haeckel ("Natural History of Creation," p. 416), "each Lichen is composed essentially of two different plants, of a low form of Alga (Nostoc, Protococcus) (Fig. 111) and of a parasitic Fungus (Ascomycetes) (Fig. 110), which is parasitic on the first, and lives off the assimilated material which this furnishes. The green chlorophyll-holding cells (gonidia), which one finds in every Lichen, belong to the Alga. The colorless threads (hyphi), on the contrary, which, thickly woven, form the principal mass of the body of the Lichen, belong to the parasitic Fungus. But always are both plant-forms—Fungus and Alga, which are considered as belonging to different classes—so firmly bound with one another, and so intimately grown together, that every one regards the Lichen as a single organism."
Notwithstanding the differences in size, color, form, reproduction, and habitat seen in this brief survey, the structure of Algae, Fungi, and Lichens has always appeared to be the same, cellular. When we compare plants apparently so distinct as mushrooms, mildews, encrusting matter of rocks, greenish layers of ponds, sea-weed, etc., the closest examination rarely reveals more than a combination of cells, no Alga, Fungus, or Lichen offering us the distinction of stem, leaves, vessels, or flowers observed in the higher plants. Botanists join, therefore, these three groups in one division, the Thallophytes or Cellular plants, a thallus being an expansion of cells.
With the Thallophytes we leave the first division of the vegetal kingdom.
CHARACEAE.
The Characeae are unique plants, including the Nitella and Chara, which differ only in the structure of their tubes, the Chara having a cortical layer in addition to the simple tubes of Nitella. The Chara is found in ponds and ditches, being composed of elongated tubes giving off at intervals whorls of branches which look very much like small green candelabra. The Chara (Fig. 112) is always an object of interest to the microscopist, as exhibiting the circulation of the chlorophyll, or green matter, the globules of which may be seen ascending and descending along the sides of the tubes. The Characeae in their structure and general appearance resemble the Green Algae, while their reproductive apparatus is more like that of the Mosses. This consists of an orange-colored globule and an oval-shaped nuclule. The globule (Fig. 112, C) bursting, a number of spiral filaments come forth, which move about in the water; the nuclule (Fig. 112, D), falling off in time, gives rise to a new Chara. The globule and nuclule are supposed to be the homologues of the, reproductive organs of the higher plants. The Characeae are isolated plants, seeming to be the only remnant of a group once more numerous: they stand on a boundary-line, so to speak, separating the Green Algae from the Hepaticae. Probably extinct plants allied to the Chara gave rise to the Hepaticae, and indirectly through them to the Mosses and Ferns.
HEPATICAE.
The Hepaticse, commonly known as Liverworts, are small plants of varied forms found on damp ground, moist parts of trees, or floating on the water. The lowest representatives consist simply of a single layer of cells forming a green membrane or patch, as in Anthroceros (Fig. 113), or there is a double layer of cells, as seen in Sphaerocarpus. In Marchantia (Fig. 114) the layers of cells are more numerous and thicker than in the lower forms just mentioned, and the upper and lower surfaces are clothed with a skin or epidermis, on the upper surface of which stomata are seen; stomata are holes in the epidermis through which air can pass from the outside of the plant to the inside. In the middle of the frond or body of the Riccia a distinct line or midrib is seen. This line in the Jungermannia (Fig. 116) becomes a well-defined stem, with leafy appendages on each side. The Jungermanniae are therefore the first plants in which we meet with the structures so characteristic of higher plants, viz., the stem and leaves; the apparent stems of the Fucoidae and Floridae being composed only of a greater number of denser cells, not essentially different from the adjacent parts either in structure or function. While the higher forms of Liverworts, in having stems and leaves, exhibit a marked progress, the lower forms in their cellular structure differ in no way from the Green Algae. The structure of the reproductive apparatus, however, in all Liverworts is much more complex than that of the Algae. In the concave receptacles, supported by stalks, as seen in Marchantia (Fig. 114), are found oval cellular bodies, the so-called Antheridia (Fig. 120, C), which contain spiral filaments (Fig. 120, D) capable of moving after having escaped from the Antheridia. The convex-lobed bodies terminating the stalks of the same plant (Fig. 115) contain flask-shaped bodies, the Archegonia (Fig. 120, A), inside of which will be found the embryo-cell (Fig. 120, B). The embryo-cell, after the contact of the spiral filament, is changed into the Sporangium, or case which contains the spores, from which the new plant will be developed.
The Hepaticae, or Liverworts, seem to be transitional plants, leading up from the Green Algae and Characeae to the Mosses and Ferns, they representing, probably, the common stem from which the roots of the Mosses and Ferns have diverged.
MOSSES.
The beautiful green velvety carpeting of woods commonly known as Mosses (Figs. 118, 119), growing most luxuriantly in damp, shady places, so useful from freely absorbing and retaining moisture, to be given out in time of drought, is made up of small delicate plants, each individual consisting of a stem and leaves, exhibiting under a low magnifying power a great variety and beauty of form. While Mosses, in the arrangement of their stem and leaves, differ greatly from the Jungermanniae, one group of them, the Hypoterygiae (Fig. 117) furnish perfectly the transition; the erect stem and leaves of the Hypoterygiae agreeing in structure with the procumbent one of Jungermanniae. The reproductive apparatus of the Hypoterygiae, however, is like that of Mosses generally. This consists, as in Hepaticae, of Archegonia and Antheridia. The Archegonia are flask-shaped bodies containing the embryo-cell. The Antheridia (Fig. 120, C) are oval cellular bodies, having inside the spiral filament. (Fig. 120, D.) The embryo-cell (Fig. 120, B), by the contact of the spiral filament, is changed in Mosses, however, into a stalk supporting an urn-shaped body. In this urn are produced the spores, which do not at once reproduce the new Moss, but protrude a confervoid
growth, the so-called Protonema, a structure very like that 
of an Alga or Fungus. In its Protonema stage the Moss is only a cellular plant, a Thallophyte. Later, out of the Protonema is developed the true Moss, with its stem, leaves, and reproductive organs.
The Mosses have probably descended, through forms like the Hypoterygiae, from the Jungermanniae.
FILICALES.
The so-called Horse-tails of ditches, etc., our common Ferns, the aquatic plants known as Pillwort and Club-moss, are generally considered by botanists as representing four different orders of _the class Filicales. While Ferns, etc. are as highly organized as Mosses, in having stems and leaves, the vascularity of their stem exhibits a considerable advance as compared with the same structure in Mosses. The Fern and Horse-tail, though differing in appearance, are usually associated, since their reproduction is the same. The Pillwort and Club-moss, agreeing in their reproduction, differ, however, from that observed in the Horse-tail and Fern: hence their frequent union. The Filicales of the present day play an inferior part as compared with those of past time. Tropical climates even do not give us an idea of what the class once was, as regards their size, variety, and importance in the economy of nature. They are sometimes called Acrogens, or summit-growers. We will examine now a little more closely the living Filicales, leaving for the chapter on Geology the account of those forms that have died out.
EQUISETACEAE.
The Horse-tail, or Equisetum (Fig. 121), is a very common plant, abounding in ditches, woods, marshes, etc., and is readily distinguished by its very characteristic appearance: though small in temperate regions, in the tropics it attains a size of fifteen or sixteen feet. The Horse-tail is composed of a series of hollow tubes joined end to end, the articulations being separable, and these tubes are marked externally by furrows running longitudinally. In place of leaves, the Equisetum exhibits green-colored branchlets; it has also rhizomes, or underground stems, sometimes extending to the depth of many feet. The spores are contained in a spike-shaped or conical cap, terminating the stem of the plant; the spores produce a cellular structure, the Prothallus, from which the new Equisetum will be developed: this kind of reproduction is seen in the Ferns, of which we will presently speak. There is found in all parts of the Horse-tail such a large amount of silex that the plant becomes important in a commercial point of view, it being much used for polishing.
FILICES
Ferns are not only interesting to botanists on account of their structure and reproduction, but also equally attractive to the laity, their graceful stems and exquisite leaves furnishing specimens for the greenhouse and ornaments for the parlor. These beautiful plants are abundantly found in damp, shady places, though a damp soil and moist climate seem more necessary than shade for their luxuriant growth. If an oblique section (Fig. 123) of the stem of a Fern be magnified, the most important features observed are the vessels or ducts running down the middle of the stem, which have in them some woody tissue. So characteristic is the presence of vessels in the higher flowering plants, that Ferns, from having these organs, are often associated with them. At certain seasons there are seen, generally on the under surface of the leaf of a Fern, small bodies usually supported on stems, known as Sori. (Fig. 124, a.) Each sorus, when magnified, is seen to consist of numerous capsules (thecae); these capsules contain the spores. The spores are angular-shaped bodies (Fig. 125, a), with an external coat of a brownish color, which is variously marked, like the pollen of higher plants. The spores, when placed in a damp surface and exposed to the proper influences of heat and light, germinate; that is, the angles of the spore are rounded off, the internal coat of the spore is then protruded, becoming the root-fibre (Fig. 125, b); the outer coat of the spore bursting, the inner coat grows in an opposite direction to that of the root-fibre as an elongated filament (Fig. 125, c); cell after cell is added in a longitudinal direction, the plant soon resembling an Alga. After a time, however, the cells are produced transversely as well as longitudinally, resulting in the formation of a flattened leaf-like expansion (Fig. 125, d), a cellular structure, the so-called Prothallus, which can scarcely be distinguished from a young Marchantia. In this Prothallus are developed Archegonia and Antheridia: the union of the embryo-cell of the Archegonia and the spiral filament of the Antheridia gives rise to the new Fern, which may be seen growing out of the Prothallus (Fig. 126), which soon passes away. These two stages in the life of a Fern represent two distinct plants. The Prothallus stage is a cellular plant closely resembling a young Marchantia, which is later transformed into a stem- and leaf-bearing plant. The growth of the Horse-tail offers the same metamorphosis; spores producing a Prothallus from which the Horse-tail is developed. While the Mosses are probably the posterity of Jungermannia-like plants, the Ferns have most likely descended from forms allied to Marchantia; this view being based on the fact of the Fern passing through a Marchantia-like stage, with similar reproductive organs.
RHIZOCARPAE.
The RhizocarpjE, a group of minute water-plants, are represented by four genera found in different parts of the world, of which the Pillwort and Pepperwort are probably the best-known, these plants being rather botanical curiosities than objects of every-day attention. They are inconspicuous plants, growing in the mud at the edges of pools, or floating about in stagnant water. A plant of this group (Marsilea) (Fig. 127) consists of a creeping stem; from the upper side rise stalks ending in leaves, from the lower hang roots; at the base of the stalks, near the roots, are seen the spore-cases (sporocarps): hence the name of this order, Rhizos- (root) carpae (fruit). The spore-cases of the Pill-wort (Pilularia) and Pepperwort (Marsilea) contain both small and large spores. In Salvinia and Azolla the large and small spores have each their special spore-case. The importance of this arrangement of the reproductive apparatus in Salvinia and Azolla will appear when speaking of the flowering plants. The development of the future Rhizocarp from the large and small spores is the same as that observed in the Club-mosses, to which we will now turn.
LYCOPODIACEAE.
The Lycopodiaceae (Fig. 128), or Club-mosses, are delicate creeping plants, producing leafy-like branches, resembling in their general appearance Mosses, though differing from them in structure and manner of reproduction. The Club-mosses of the present day are small plants; this was not always the case, the order being represented in past time by trees, attaining the height of sixty feet, with gigantic roots, giving the vegetation of that period a very characteristic appearance. The stem of the Lycopodiaceae exhibits the same vascular and cellular structure noticed in the Ferns. In the Isoetes (a Lycopod) we see, for the first time in our brief survey of the vegetal kingdom, a stem presenting woody layers one inside of the other, one of the distinguishing features of trees hke the Oak, Walnut, Chestnut, Pine, Fir, Cycas. This fact is an important one, as will appear later. The reproduction of the Lycopodiaceae and Rhizocarpse differs from that of any plants of which we have yet spoken. There are found in the Lycopodiaceae both large and small spore-cases, of which the former (Fig. 128) contain only four large spores, the latter (Fig. 128) many small ones. In Selaginella the leaves are spike-shaped, and at the base of the leaf is found either a large or small spore-case. Each spore of the large spore-case may produce within its cavity a Prothallus like that of the Fern; but it will be remembered that the Prothallus of the Fern is produced outside of the spore, whereas the Prothallus of the Lycopod is developed inside the large spore. In the Prothallus of the Lycopod, Archegonia, with their embryo-cells, alone are found; the Antheridia, with their spiral filaments, coming only from the small spores. Finally the large spore bursts, freeing its Prothallus. The spiral filament of the Antheridium of the small spore, coming in contact with the embryo-cell in the Archegonium in the Prothallus of the large spore, gives rise to the new Lycopod, which, in Selaginella, is a little stem supporting two leaves, one on each side. (Fig. 129.) This kind of reproduction is seen in the Rhizocarpae. By comparing the reproduction noticed in the Fern, Horse-tail, Rhizocarp, and Lycopod, the following series becomes apparent: the Ferns and Horse-tails produce one kind of spore; from this spore is developed a Prothallus containing both Archegonia with their embryo-cells, and Antheridia with their spiral filaments. The Rhizocarpae and Lycopodiaceae produce two kinds of spores, large and small; in the Pillwort and Pepperwort the large and small spores are found in the same spore-case, but in the Salvinia and Azolla the large and small spores have their special spore-cases, as in the Lycopodiaceae; the large spore alone develops the Prothallus with Archegonia and embryo-cells, the small spores alone producing Antheridia with spiral filaments. The reproduction, however, of the Horse-tail, Fern, Rhizocarp, or Lycopod is always due to the contact of the spiral filament of the Antheridium with the embryo-cell of the Archegonium, the new plant growing always from a Prothallus. The Lycopodiaceae appeared on the earth later than the Ferns, and have probably come from them, being closely related at the present time by intermediate forms (Opioglossae). The Rhizocarpae may be regarded as aquatic Lycopods. The structure of the stem and reproductive apparatus, and the form of the embryo, are striking proofs of the truth of the view that the Lycopodiaceae are the intermediate forms, the links uniting the Flowerless and Flowering plants. The importance of the facts just mentioned will be better appreciated when the Lycopodiaceae are compared with the simplest of flowering plants. We leave now the Flowerless plants, or Cryptogamia, and turn to the Flowering plants, or Phanerogamia.
PHANEROGAMIA.
Flowers, among the most beautiful of nature's works, are always interesting to the laity and the botanist, offering objects of ornament and beauty to the one, and subjects for study and admiration to the other. The flower is the reproductive apparatus of the higher plants, made up of the organs by which the seed is produced, fertilized, and converted into the embryo plant. If we examine the flower of the Violet (Yellow Violet) (Fig. 130), the green cup-like arrangement of leaves first deserves our attention; this is known as the calyx, and the leaves composing it are called sepals. Within the calyx is seen another whorl of yellow leaves, known as petals; their union forms the corolla. Springing from the middle of the calyx and corolla, and standing erect, is seen a delicate tube, the pistil. Surrounding the pistil, and differing from it in appearance, are found the stamens. If the pistil is examined separately (Fig. 132), it is seen to be composed of the following parts: the head or stigma, the stalk or style, and the ovary. The ovary contains the ovule, or future seed, and if the ovule be magnified it is seen to contain the embryo-sac, and within the embryo-sac is found the germinal vesicle. The germinal vesicle is the rudiment of the future plant. The stamens, or stalks, surrounding the pistil, are composed of the stems or filaments supporting the anthers or little heads. The anthers contain the pollen, or fertilizing principle. Suppose the supreme power of Turkey to be a woman, and the Sultana to have a harem of men, such a condition of social life would represent what is seen in the Violet, or better in a section of the Morning-glory (Fig. 131), where the imaginary Sultana is realized in the pistil, the harem of men in the stamens. The pollen produced in the anthers finds its way to the stigma, or head of the pistil; from the head it passes down through the style, or tube of the pistil, until it reaches the ovary. Piercing successively the ovary, ovule, and embryo-sac, it finally comes in contact with the germinal vesicle. From this moment the life of the new plant begins in the formation of the embryo. The flowers of the Violet and Morning-glory serve to illustrate the reproductive apparatus of many plants. If, however, the flower of the Goose-foot (Chenopodium) (Fig. 133) be compared with that of the Violet, the absence of the corolla at once strikes the attention; and if the flowers of the Bread-tree, Pine, etc. (Fig. 135, a, b) be now examined, calyx and corolla are both found wanting. Further, in trees like the Pine, etc. there is no ovary, the ovule being exposed to view resting on the edge of the leaf (Fig. 135, a); the ovule is fertilized by the falling of the pollen, style and stigma being absent as well as ovary. Plants of this kind are called, therefore, Gymnospermae, or naked seeds; whereas those having an ovary are known as Angiospermae, or seed-vessels. The flowering plants divide naturally, therefore, into these two groups. To the Gymnospermae, or plants with naked seeds, belong the Bread-tree, Zamia, and Cycas (Cycadae), the Pine, Fir, Cypress, Juniper, Cedar, and Yew (Coniferae). Among the Angiospermae, or plants whose seeds are contained in seed-vessels, are found the forest-trees, fruit-trees, grasses, roses, violets, etc.
CYCADAE.
The Cycadae are small palm-like trees (Fig. 137), or shrubs with unbranched stems, found principally in the tropical regions of Asia and America. The Bread-tree belongs to this order, supplying the Caffre bread; the Cycas of Japan produces, in its stem, a starchy matter, which is collected and eaten like sago. The Cycadae are sometimes called Palm-ferns, from their resembling Ferns as well as Palms. In past time the order was much more numerous than at present. The so-called flower of the Cycadae is very simple. The naked ovules are attached to the bases of contracted leaves: these leaves in some cases overlap each other. The stamens are found on separate leaves, which overlap each other, forming a cone. The leaves containing the ovules and stamens are found on separate plants, the series being quite distinct in the Cycadae. The reproductive apparatus of the Cycadae agrees essentially with that of the Salvinia, noticed in speaking of the Rhizocarpae, the ovule of the Cycas being homologous with the large spore of Salvinia, the pollen corresponding to the small spores. As the reproduction of the Cycas from the ovule, so far as known, is the same as that of the Coniferae, we turn now to that order.
CONIFERAE.
The Coniferae, or cone-bearing trees, are so called from their fruit being in the form of cones, as in the Pines; "these cones are made up of flat scales regularly overlapping each other, and pressed together in the form of a spike or head; each scale bears one or two naked seeds in its inner face." "The pollen is contained in the substance of a body that retains in some degree its leafy type, and an assemblage of such bodies forms the 'catkin.'" In the Cypress we have cells (corresponding to stamens) at the edge of the leaf The leaves of Selaginella (a Cycopod), with their large and small spores (Figs. 136, 137), are as much flowers as the leaves of Coniferae with their organs. The Coniferae are invaluable to man, as including the most important of the timber-trees of cold countries, and furnishing the turpentines, resins, pitch, tar, and Canada Balsam. Among the Coniferae are found the Pines, Fir, Spruce, Cypress, Cedars, Larch, and Juniper. At certain seasons the ovule of Coniferae develops in its interior a mass of cells, the Endosperm; later in this Endosperm appear Corpuscles; within the Corpuscle is developed the Embryonic vesicle. The Ovule, Endosperm, Corpuscle, and Embryonic vesicle are to the Coniferae and Cycadae what the Large Spore, Prothallus, Archegonium, and Embryo-cell are to the Lycopods, the pollen of the Gymnospermae corresponding to the small spores of the Lycopodiaceae: the reproductive organs of Lycopodiaceae and Gymnospermae are, therefore, essentially the same. The higher plants differ from these orders in that the embryo-sac contains the embryo-cell only; whereas, in Lycopodiaceae and Gymnospermae, a Prothallus or Endosperm with Archegonia or Corpuscles is produced, the embryo-cell appearing in the Archegonia or Corpuscles, to which there is nothing to correspond in the higher plants, which necessarily want the Prothallus or Endosperm as well. After the contact of the germinal vesicle and the pollen, the life of the new Gymnosperm begins in the formation of the embryo, which consists of a stem or radical supporting two or more leaves (Figs. 139, 138, a), called cotyledons. The embryo of the Cypress in its two cotyledons recalls that of Selaginella (a Lycopod). Those plants whose embryos have only one leaf (Fig. 140, a) or cotyledon are called Monocotyledonous, while those having two are known as Dicotyledonous. The Dicotyledonous plants further offer in their stem the destruction of pith, wood, and bark, and increase the diameter of their stem by layer after layer (Fig. 141, 1, 2, 3) of wood being added, the new layer being deposited between the old layer and the bark, this new layer growing at the expense of the Cambium, a layer (Fig. 141, C) found always between the last and most external layer of wood and the bark. Such plants are called outside growths, or Exogens. The Monocotyledonous plants, however, do not present, in their stem, the difference of pith, wood, and bark so well defined as in Exogens; the new wood being added in bundles intermingling with the old, and deposited principally towards the centre of the plant. (Fig. 142.) Such forms are called inside growths, or Endogens. The wood of an Exogen is oldest and hardest in the centre, whereas the wood of an Endogen is newest and softest towards the centre. The increase in the diameter of the trunk of an Exogen, as in the Oak, is indefinite; the stem of the Endogen, as in the Palm, is limited as regards its diameter, the tendency being rather to grow upwards. In speaking of the Lycopodiaceae, Cycadae, and Coniferae, we have noticed they have important features in common: the reproductive apparatus is essentially the same; the form of the embryo in some genera (Selaginella, Cypress) is two-leaved, or dicotyledonous; finally, there must be added to these facts the additional one of the Cycadae and Coniferae being outside growers, and of a similar exogenous mode of growth being seen in Isoetes among the Lycopodiaceae. The Lycopodiaceae are, therefore, so closely and intimately allied with the Cycadae and Coniferae that the question naturally arises, Does there really exist in Nature such a distinction as that of Flowerless and Flowering plants? The reproductive apparatus of the Lycopodiaceae is so similar to that of the Cycadae and Coniferae that it is impossible to say where the Flowerless plants end and the Flowering begin. In the first page of this chapter we used purposely the expression, translating Cryptogamia "flowerless," Phanerogamia "flowering." The word cryptos, literally translated, is "obscure," "concealed;" phaneros, "apparent," "evident;" gamos referring to the organs of reproduction. Translating literally, the Cryptogamic plants are those in which the reproductive organs are not absent, but only obscure; the Phanerogamia, those in which the reproductive organs are very evident in the form of flowers. The difference between the higher Cryptogamia and Phanerogamia is not one of kind, but only of degree, the apparent gulf between these two divisions being bridged over by the Lycopodiaceae, Cycadae, and Coniferse. The Linnaean classification is the best yet offered, expressing the real nature of plants. The Angiospermae, as previously stated, are those flowering plants whose seeds have a seed-vessel: their embryo is either Monocotyledonous or Dicotyledonous. The one-leaved or Monocotyledonous form of embryo is universally associated with the endogenous, or inside mode of growth, usually with a threefold arrangement of leaves. The Dicotyledonous or two-leaved embryo, on the contrary, characterizes all outside growers or Exogens, accompanied usually with a fivefold arrangement of leaves. The Monocotyledons include the Palms (Fig. 143), Bananas, Orchids, Lily, and the Grasses. Among the Dicotyledons are found the Oaks, Elms, the fruit-trees, and the most beautiful flowers. The flower of the different kinds of Dicotyledons offers an interesting ascending series. The flower of the Spurge, or Euphorbia, consists of only a stamen or a pistil, known as Achlamydeous, the flower being called accordingly staminate or pistillate. A slight progress is seen in the flower of the Goose-foot, Fig, Mulberry, Elm, etc., in which, however, the corolla is still undistinguishable from the calyx. Such flowers are called, therefore, Apetalae: the flowers of the Monocotyledons are of this kind. In the Bean, Clover, Violet, Geranium, etc., the corolla and calyx are distinct, but the petals forming the corolla are still more or less separated, hence they are known as Diapetalae; in the Gentian, Elder, Ash, Morning-glory, etc., the petals have united; they are known, therefore as Gamopetalee. How the different orders of the Phanerogamia are related to each other is the last question which yet remains unanswered. The structure and reproductive apparatus of the Cycadee and Coniferee would lead us to suppose that they appeared on the earth before the Monocotyledons or Dicotyledons. This view is confirmed by geological evidence, since the fossil Cycadae and Coniferse are found in great profusion at a much earlier period than that in which the Monocotyledons or Dicotyledons first appeared. The Cycadae and Coniferae are probably the posterity of a common ancestor nearly allied to the Lycopodiaceae. Among the Coniferae there is an order, the Gnetaceae, or the jointed Firs, whose structure links them on to the Monocotyledons and Dicotyledons. Some extinct Conifer, allied to the jointed Fir, was the probable common progenitor of these two orders, of which the Dicotyledons are the most complex, both as regards the structure of the stem and flower.
RESUME.
Beginning with the most minute and simplest of plants, such as are found in every pond and ditch, and comparing them with the different sea-weed, Fungi, etc., we found, notwithstanding minor differences, that their structure was essentially the same, cellular; offering no trace in their organization of stem and leaves. Passing from the cellular plants, through transitional forms, to the Liverworts, we noticed that the lower forms of this are still cellular, while the higher exhibit the beginning of a separation into stem and leaves. Forms like these lead the way to the Mosses, in which the stem and leaves are well defined. The Ferns, while agreeing with the Mosses in having stem and leaves, offer an advance in their organization, since their stem contains vessels with more or less woody tissue. Passing from the Ferns to the closely allied Club-mosses, we found in them the links binding the Flowerless with the Flowering plants. Taking up next the Cycadae and Coniferae, we saw how naturally they preceded the Endogens and Exogens. Finally, in the different kinds of Exogens we saw an ascending series, as illustrated in the flower of the Spurge, Goose-foot, Violet, Morning-glory. Our brief survey of plants may be expressed in the following conclusion: The vegetal kingdom may be represented by a tree, of which the stems and branches are the classes, orders, etc. The trunk of this tree, being composed of the simplest forms, grows gradually upwards into more complex ones, finally developing the noblest of trees, the most beautiful of flowers. We hope to show in our next chapter that the petrified remains of the animal and vegetal kingdoms offer such a progress from lower to higher forms.
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