CHAPTER VII.

MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

203. FROM those simple Protophytes, whose minuteness causes their entire fabrics to be fitting objects for Microscopic examination, we pass to those higher forms of Vegetable life, whose larger dimensions require that they should be analyzed (so to speak) by the examination of their separate parts. And in the present chapter, we shall bring under notice some of the principal points of interest to the Microscopist, which are presented by the Cryptogamic series; commencing with those simpler Alge, which scarcely rank higher than some of the Protophytes already described; and ending with the Ferns and their allies, which closely abut upon the Phanerogamia or Flowering Plants. In ascending this series, we shall have to notice a gradual differentiation of organs; those set apart for Reproduction being in the first place separated from those appropriated to Nutrition (as we have already seen them to be in the Characea); and the principal parts of the Nutritive apparatus, which are at first so blended together that no real distinction exists between root, stem, and leaf, being progressively evolved on types more and more peculiar to each respectively, and having their functions more and more limited to themselves alone. Hence

we find a differentiation, not merely in the external form, but also in the intimate structure of organs; its degree bearing a close correspondence to the degree in which their functions are respectively specialized or limited to particular actions. Thus in the simple Ulva (Fig. 104), whatever may be the extent of the frond, every part has exactly the same structure, and performs the same actions, as every other part; living for and by itself alone. In Batrachospermum (Fig. 110), we have seen a definite arrangement of branches upon an axis of growth; and while the branches are formed of simple necklace

FIG. 113.

Mesogloia vermicularis.

like rows of rounded cells, the cells of the stem are elongated and adhere to one another by flattened ends.

This kind of dif

ferentiation is seen to be carried to a still greater extent in Mesogloia (Fig. 113); a plant which may be considered as one of the connecting links between such Protophytes as Batrachospermea -which it resembles in general plan of structure, and the Fucoid Algae, which it resembles in fructification.

204. When we pass to the higher Sea-weeds, such as the common Fucus and Laminaria, we observe a certain foreshadowing of the distinction between root, stem, and leaf; but this distinction is but very imperfectly carried out, the root-like and stem-like portions serving for little else than the mechanical attachment of the leaf-like part of the plant, and each still absorbing and assimilating its own nutriment, so that no transmission of fluid takes place from one portion of the fabric to another. Hence we find that there is not yet any departure from the simple cellular type of structure; the only modification being, that the several layers of cells, where many exist, are of different sizes and shapes, the texture being usually closer on the exterior and looser within; and that the texture of the stem and roots is denser than that of the expanded fronds. This simple cellular type of structure is maintained through all but the highest Cryptogamia; for it is not until we come to the Mosses, that the differentiation of stem, root, and leaf is established; and even in these it is not so fully carried out, as to require a provision for the free transmission of fluid from one part to another; whilst the scale of their fabrics is not such as to render it necessary that their softer parts should be supported by a tissue of peculiar density. But in the group of Ferns, which, notwithstanding their complete adhesion to the Cryptogamic type of Reproduction, have the general form of the higher plants, and even attain the size and bearing of trees, we find the leaves separated from the roots by the intervention of a stem; and in this stem, as also in the leaf-stalks prolonged from it, we find, interposed in the midst of the cellular tissue which forms their principal substance, two new forms of structure,-namely, woody fibre which serves to give strength and support to the stem and to the organs it bears, and ducts through which the liquid absorbed by the roots may be readily conveyed to the leaves.

205. The group of Melanospermous or olive-green Sea-weeds, which, in the family Fucaceae, exhibits the highest type of Algal structure, presents us with the lowest in the family Ectocarpacea; which, notwithstanding, contains some of the most elegant and delicate structures that are anywhere to be found in the group, the full beauty of which can only be discerned by the microscope. Such is the case, for example, with the Sphacelaria, a small and delicate sea-weed, which is very commonly found parasitic upon larger Algæ, either near low-water mark, or altogether submerged; its general form being remarkably charac terized by a symmetry that extends also to the individual branches (Fig. 114), the ends of which, however, have a decayed

look, that seems to have suggested the name of the genus (from the Greek gazelos, gangrene). The study of the higher and larger members of this group, has recently come to present a new and very attractive source of interest to the Microscopist, in consequence of the discovery of the truly sexual nature of their fructification; and we shall take that of a common species of Fucus as the type of that of the order generally. The "receptacles" which are borne at the extremities of the fronds, here contain both "sperm-cells" and "germ-cells;" in some other species, however, they are disposed in different receptacles on the same plant; whilst in the commonest of all, F. vesiculosus (bladder-wrack), they are limited to different individuals.' When a section is made through one of the flattened receptacles of F. platycarpus, its interior is seen to be a nearly globular cavity (Fig. 115), lined with filament

FIG. 114.

FIG. 115.

Fig. 114. Terminal portion of branch of Sphacelaria cirrhosa.

Fig. 115. Vertical Section of receptacle of Fucus platycarpus, lined with filaments, among which lie the antheridial cells, and the sporangia containing octospores.

ous cells, some of which are greatly elongated, so as to project through the pore by which the cavity opens on the surface. Among these are to be distinguished, towards the period of their

It was at first stated by MM. Thuret and Decaisne, that this species was sometimes diacious, sometimes hermaphrodite; but they now consider the hermaphrodite form to be a distinct species, the F. platycarpus described above.

maturity, certain filaments (Fig. 116, A) whose granular contents acquire an orange hue, and gradually shape themselves into oval bodies (B), each with an orange-colored spot, and two long

Antheridia and antherozoids of Fucus platycarpus :—A, branching articulated hairs, detached from the walls of the receptacle, bearing antheridia in different stages of development; B, antherozoids, some of them free, others still included in their antheridial cells.

thread-like appendages, which, when discharged by the rupture of the containing cell, have for a time a rapid undulatory motion, whereby these autherozoids are diffused through the surrounding liquid. Lying amidst the filamentous mass, near the walls of the cavity, are seen (Fig. 115) numerous dark pear-shaped bodies, which are the sporangia, or parent cells of the "germ-cells." Each of these sporangia gives origin, by duplicative subdivision, to a cluster of eight cells, which is thence known as an "octospore;" and these are liberated from their envelopes, before the act of fertilization takes place. This act consists in the swarming of the antherozoids over the surface of the germ-cells, to which they communicate a rotatory motion by the vibration of their own filaments; it takes place within the receptacles in the hermaphrodite Fuci, so that the spores do not make their exit from the cavity until after they have been fecundated; but in the monœcious and dioecious species, each kind of receptacle separately discharges its contents, which come into mutual contact on their exterior. The antheridial cells are usually ejected entire, but soon rupture, so as to give exit to their filaments; the sporangia of the female receptacles discharge their globular octospores within the receptacle; and these, soon after passing forth, liberate their separate spores, which speedily meet with antherozoids and are fecundated by them. The spores, when fertilized, soon acquire a new and firmer envelope; and under favorable circumstances they speedily begin to develope themselves into new plants. The first change that is seen in them, is

the projection and narrowing of one end into a kind of footstalk, by which the spore attaches itself, its form passing from the globular to the pear-shaped; a partition is speedily observable in its interior, its single cell being subdivided into two; and by a continuation of a like process of duplication, first a filament, and then a frondose expansion, is produced, which_gradually evolves itself into the likeness of the parent plant. The whole of this process may be watched without difficulty, by obtaining specimens of F. vesiculosus at the period at which the fructification is shown to be mature, by the recent discharge of the contents of the conceptacles in little gelatinous masses on their orifices; for if some of the spores, which have been set free from the olive-green (female) receptacles, be placed in a drop of sea-water in a very shallow cell, and a small quantity of the mass of antherozoids set free from the orange-yellow (male) recepta cles, be mingled with the fluid, they will speedily be observed, with the aid of a magnifying power of 200 or 250 diameters, to go through the actions just described; and the subsequent processes of germination may be watched by means of the "growing-slide." The winter months, from December to March, are the most favorable for the observation of these phenomena; but where the Fuci abound, some individuals will usually be found in fructification at almost any period of the year. Even in the Fucaceae, according to recent observations, a multiplication by zoospores, like that of the Ulvacea (§ 195), still takes place; these bodies being produced within certain of the cells that form the superficial layer of the frond, and swimming about freely for a time after their emission, until they fix themselves and begin to grow. That they are to be considered gemmæ, and not as generative products, appears certain from the fact that they will vegetate without the assistance of any other bodies; whereas the antherozoids of themselves never come to anything, and the octospores undergo no further changes, but decay away (as M. Thuret has experimentally ascertained), if not fecundated by the antherozoids.

206. Among the Rhodospermeæ, or red Sea-weeds, also, we find various simple but most beautiful forms, which connect this group with the more elevated Protophytes, especially with the family Chatophoraceae; such delicate feathery or leaf-like fronds belong, for the most part to the family Ceramiacea, some members of which are found upon every part of our coasts, attached either to rocks or stones, or to larger Alge, and often themselves affording an attachment to Zoophytes and Bryozoa. They chiefly live in deeper water than the other sea-weeds; and their richest tints are only exhibited, when they grow under the shade of projecting rocks or of larger dark-colored Algæ. Hence in growing

'If a cell be not employed, the drop should not be covered, unless some precaution be taken to keep the pressure of the thin glass from the minute bodies beneath, whose movements it will otherwise impede.