Part 16

496. =Azolla= is a little floating plant, looking like a small Liverwort or Moss. Its branches are covered with minute and scale-shaped leaves. On the under side of the branches are found egg-shaped thin-walled sporocarps of two kinds. The small ones open across and discharge microspores; the larger burst irregularly, and bring to view globose spore-cases, attached to the bottom of the sporocarp by a slender stalk. These delicate spore-cases burst and set free about four macrospores, which are fertilized at germination, in the manner of the Pillworts and Quillworts. (See Fig. 521-526.)

497. =Cellular Cryptogams= (483) are so called because composed, even in their higher forms, of cellular tissue only, without proper wood-cells or vessels. Many of the lower kinds are mere plates, or ribbons, or simple rows of cells, or even single cells. But their highest orders follow the plan of Ferns and phanerogamous plants in having stem and leaves for their upward growth, and commonly roots, or at least rootlets, to attach them to the soil, or to trunks, or to other bodies on which they grow. Plants of this grade are chiefly Mosses. So as a whole they take the name of

498. =Bryophyta, Bryophytes= in English form, Bryum being the Greek name of a Moss. These plants are of two principal kinds: true Mosses (_Musci_, which is their Latin name in the plural); and Hepatic Mosses, or Liverworts (_Hepaticae_).

499. =Mosses or Musci.= The pale Peat-mosses (species of Sphagnum, the principal component of sphagnous bogs) and the strong-growing Hair-cap Moss (Polytrichum) are among the larger and commoner representatives of this numerous family; while Fountain Moss (Fontinalis) in running water sometimes attains the length of a yard or more. On the other hand, some are barely individually distinguishable to the naked eye. Fig. 527 represents a common little Moss, enlarged to about twelve times its natural size; and by its side is part of a leaf, much magnified, showing that it is composed of cellular tissue (parenchyma-cells) only. The leaves of Mosses are always simple, distinct, and sessile on the stem. The fructification is an urn-shaped spore-case, in this as in most cases raised on a slender stalk. The spore-case loosely bears on its summit a thin and pointed cap, like a candle-extinguisher, called a _Calyptra_. Detaching this, it is found that the spore-case is like a pyxis (376), that is, the top at maturity comes off as a lid (_Operculum_); and that the interior is filled with a green powder, the spores, which are discharged through the open mouth. In most Mosses there is a fringe of one or two rows of teeth or membrane around this mouth or orifice, the _Peristome_. When moist the peristome closes hygrometrically over the orifice more or less; when drier the teeth or processes commonly bend outward or recurve; and then the spores more readily escape. In Hair-cap Moss a membrane is stretched quite across the mouth, like a drum-head, retaining the spores until this wears away. See Figures 527-541 for details.

500. Fertilization in Mosses is by the analogues of stamens and pistils, which are hidden in the axils of leaves, or in the cluster of leaves at the end of the stem. The analogue of the anther (_Antheridium_) is a cellular sac, which in bursting discharges innumerable delicate cells floating in a mucilaginous liquid; each of these bursts and sets free a vibratile self-moving thread. These threads, one or more, reach the orifice of the pistil-shaped body, the _Pistillidium_, and act upon a particular cell at its base within. This cell in its growth develops into the spore-case and its stalk (when there is any), carrying on its summit the wall of the pistillidium, which becomes the calyptra.

501. =Liverworts or Hepatic Mosses= (_Hepaticae_) in some kinds resemble true Mosses, having distinct stem and leaves, although their leaves occasionally run together; while in others there is no distinction of stem and leaf, but the whole plant is a leaf-like body, which produces rootlets on the lower face and its fructification on the upper. Those of the moss-like kind (sometimes called Scale-Mosses) have their tender spore-cases splitting into four valves; and with their spores are intermixed some slender spiral and very hygrometric threads (called _Elaters_) which are thought to aid in the dispersion of the spores. (Fig. 542-544.)

502. Marchantia, the commonest and largest of the true Liverworts, forms large green plates or fronds on damp and shady ground, and sends up from some part of the upper face a stout stalk, ending in a several-lobed umbrella-shaped body, under the lobes of which hang several thin-walled spore-cases, which burst open and discharge spores and elaters. Riccia natans (Fig. 545) consists of wedge-shaped or heart-shaped fronds, which float free in pools of still water. The under face bears copious rootlets; in the substance of the upper face are the spore-cases, their pointed tips merely projecting: there they burst open, and discharge their spores. These are comparatively few and large, and are in fours; so they are very like the macrospores of Pillworts or Quillworts.

503. =Thallophyta, or Thallophytes= in English form. This is the name for the lower class of Cellular Cryptogams,--plants in which there is no marked distinction into root, stem, and leaves. Roots in any proper sense they never have, as organs for absorbing, although some of the larger Seaweeds (such as the Sea Colander, Fig. 553) have them as holdfasts. Instead of axis and foliage, there is a stratum of frond, in such plants commonly called a THALLUS (by a strained use of a Greek and Latin word which means a green shoot or bough), which may have any kind of form, leaf-like, stem-like, branchy, extended to a flat plate, or gathered into a sphere, or drawn out into threads, or reduced to a single row of cells, or even reduced to single cells. Indeed, Thallophytes are so multifarious, so numerous in kinds, so protean in their stages and transformations, so recondite in their fructification, and many so microscopic in size, either of the plant itself or its essential organs, that they have to be elaborately described in separate books and made subjects of special study.

504. Nevertheless, it may be well to try to give some general idea of what Algae and Lichens and Fungi are. Linnaeus had them all under the orders of Algae and Fungi. Afterwards the Lichens were separated; but of late it has been made most probable that a Lichen consists of an Alga and a Fungus conjoined. At least it must be so in some of the ambiguous forms. Botanists are in the way of bringing out new classifications of the Thallophytes, as they come to understand their structure and relations better. Here, it need only be said that

505. Lichens live in the air, that is, on the ground, or on rocks, trunks, walls, and the like, and grow when moistened by rains. They assimilate air, water, and some earthy matter, just as do ordinary plants. Algae, or Seaweeds, live in water, and live the same kind of life as do ordinary plants. Fungi, whatever medium they inhabit, live as animals do, upon organic matter,--upon what other plants have assimilated, or upon the products of their decay. True as these general distinctions are, it is no less true that these orders run together in their lowest forms; and that Algae and Fungi may be traced down into forms so low and simple that no clear line can be drawn between them; and even into forms of which it is uncertain whether they should be called plants or animals. It is as well to say that they are not high enough in rank to be distinctively either the one or the other. On the other hand there is a peculiar group of plants, which in simplicity of composition resemble the simpler Algae, while in fructification and in the arrangements of their simple cells into stem and branches they seem to be of a higher order, viz.:--

506. =Characeae.= These are aquatic herbs, of considerable size, abounding in ponds. The simpler kinds (Nitella) have the stem formed of a single row of tubular cells, and at the nodes, or junction of the cells, a whorl of similar branches. Chara (Fig. 550-552) is the same, except that the cells which make up the stem and the principal branches are strengthened by a coating of many smaller tubular cells, applied to the surface of the main or central cell. The fructification consists of a globular sporocarp of considerable size, which is spirally enwrapped by tubular cells twisted around it: by the side of this is a smaller and globular antheridium. The latter breaks up into eight shield-shaped pieces, with an internal stalk, and bearing long and ribbon shaped filaments, which consist of a row of delicate cells, each of which discharges a free-moving microscopic thread (the analogue of the pollen or pollen-tube), nearly in the manner of Ferns and Mosses. One of these threads reaches and fertilizes a cell at the apex of the nucleus or solid body of the sporocarp. This subsequently germinates and forms a new individual.

507. =Algae or Seaweeds.= The proper Seaweeds may be studied by the aid of Professor Farlow's "Marine Algae of New England;" the fresh-water species, by Prof. H. C. Woods's "Fresh-water Algae of North America," a larger and less accessible volume. A few common forms are here very briefly mentioned and illustrated, to give an idea of the family. But they are of almost endless diversity.

508. The common Rockweed (Fucus vesiculosus, Fig. 554, abounding between high and low water mark on the coast), the rarer Sea Colander (Agarum Turneri, Fig. 553), and Laminaria, of which the larger forms are called Devil's Aprons, are good representatives of the olive green or brownish Seaweeds. They are attached either by a disk-like base or by root-like holdfasts to the rocks or stones on which they grow.

509. The hollow and inflated places in the Fucus vesiculosus or Rockweed (Fig. 554) are air-bladders for buoyancy. The fructification forms in the substance of the tips of the frond: the rough dots mark the places where the conceptacles open. The spores and the fertilizing cells are in different plants. Sections of the two kinds of conceptacles are given in Fig. 555 and 556. The contents of the conceptacles are discharged through a small orifice which in each figure is at the margin of the page. The large spores are formed eight together in a mother-cell. The minute motile filaments of the antheridia fertilize the large spores after injection into the water: and then the latter promptly acquire a cell-wall and germinate.

510. The Florideae or Rose-red series of marine Algae (which, however, are sometimes green or brownish) are the most attractive to amateurs. The delicate Porphyra or Laver is in some countries eaten as a delicacy, and the cartilaginous Chondrus crispus has been largely used for jelly. Besides their conceptacles, which contain true spores (Fig. 560), they mostly have a fructification in _Tetraspores_, that is, of spores originating in fours (Fig. 559).

511. The Grass-green Algae sometimes form broad membranous fronds, such as those of the common Ulva of the sea-shore, but most of them form mere threads, either simple or branched. To this division belong almost all the Fresh-water Algae, such as those which constitute the silky threads or green slime of running streams or standing pools, and which were all called Confervas before their immense diversity was known. Some are formed of a single row of cells, developed each from the end of another. Others branch, the top of one cell producing more than one new one (Fig. 564). Others, of a kind which is very common in fresh water, simple threads made of a line of cells, have the chlorophyll and protoplasm of each cell arranged in spiral lines or bands. They form spores in a peculiar way, which gives to this family the designation of conjugating Algae.

512. At a certain time two parallel threads approach each other more closely; contiguous parts of a cell of each thread bulge or grow out, and unite when they meet; the cell-wall partitions between them are absorbed so as to open a free communication; the spiral band of green matter in both cells breaks up; the whole of that of one cell passes over into the other; and of the united contents a large green spore is formed. Soon the old cells decay, and the spore set free is ready to germinate. Fig. 565 represents several stages of the conjugating process, which, however, would never be found all together like this in one pair of threads.

513. Desmids and Diatomes, which are microscopic one-celled plants of the same class, conjugate in the same way, as is shown in a Closterium by Fig. 566, 567. Here the whole living contents of two individuals are incorporated into one spore, for a fresh start. A reproduction which costs the life of two individuals to make a single new one would be fatal to the species if there were not a provision for multiplication by the prompt division of the new-formed individual into two, and these again into two, and so on in geometrical ratio. And the costly process would be meaningless if there were not some real advantage in such a fresh start, that is, in sexes.

514. There are other Algae of the grass-green series which consist of single cells, but which by continued growth form plants of considerable size. Three kinds of these are represented in Fig. 568-574.

515. =Lichens=, Latin _Lichenes_, are to be studied in the works of the late Professor Tuckerman, but a popular exposition is greatly needed. The subjoined illustrations (Fig. 575-580) may simply indicate what some of the commoner forms are like. The cup, or shield-shaped spot, or knob, which bears the fructification is named the _Apothecium_. This is mainly composed of slender sacs (_Asci_), having thread-shaped cells intermixed; and each ascus contains few or several spores, which are commonly double or treble. Most Lichens are flat expansions of grayish hue; some of them foliaceous in texture, but never of bright green color; more are crustaceous; some are wholly pulverulent and nearly formless. But in several the vegetation lengthens into an axis (as in Fig. 580), or imitates stem and branches or threads, as in the Reindeer-Moss on the ground in our northern woods, and the Usnea hanging from the boughs of old trees overhead.

516. =Fungi.= For this immense and greatly diversified class, it must here suffice to indicate the parts of a Mushroom, a Sphaeria, and of one or two common Moulds. The true vegetation of common Fungi consists of slender cells which form what is called a _Mycelium_. These filamentous cells lengthen and branch, growing by the absorption through their whole surface of the decaying, or organizable, or living matter which they feed upon. In a Mushroom (Agaricus), a knobby mass is at length formed, which develops into a stout stalk (_Stipe_), bearing the cap (_Pileus_): the under side of the cap is covered by the _Hymenium_, in this genus consisting of radiating plates, the gills or _Lamellae_; and these bear the powdery spores in immense numbers. Under the microscope, the gills are found to be studded with projecting cells, each of which, at the top, produces four stalked spores. These form the powder which collects on a sheet of paper upon which a mature Mushroom is allowed to rest for a day or two. (Fig. 581-586.)

517. The esculent Morel, also Sphaeria (Fig. 585, 586), and many other Fungi bear their spores in sacs (asci) exactly in the manner of Lichens (515).

518. Of the Moulds, one of the commoner is the Bread-Mould (Fig. 587). In fruiting it sends up a slender stalk, which bears a globular sac; this bursts at maturity and discharges innumerable spores. The blue Cheese-Mould (Fig. 588) bears a cluster of branches at top, each of which is a row of naked spores, like a string of beads, all breaking apart at maturity. Botrytis (Fig. 589), the fruiting stalk of which branches, and each branch is tipped with a spore, is one of the many moulds which live and feed upon the juices of other plants or of animals, and are often very destructive. The extremely numerous kinds of smut, rust, mildew, the ferments, bacteria, and the like, many of them very destructive to other vegetable and to animal life, are also low forms of the class of Fungi.[1]

FOOTNOTES:

[1] The "Introduction to Cryptogamous Botany," or third volume of "The Botanical Text Book," now in preparation by the author's colleague, Professor Farlow, will be the proper guide in the study of the Flowerless Plants, especially of the Algae and Fungi.

SECTION XVIII. CLASSIFICATION AND NOMENCLATURE.

519. Classification, in botany, is the consideration of plants in respect to their kinds and relationships. Some system of Nomenclature, or naming, is necessary for fixing and expressing botanical knowledge so as to make it available. The vast multiplicity of plants and the various degrees of their relationship imperatively require order and system, not only as to _names_ for designating the kinds of plants, but also as to _terms_ for defining their differences. Nomenclature is concerned with the names of plants. Terminology supplies names of organs or parts, and terms to designate their differences.

Sec. 1. KINDS AND RELATIONSHIP.