ANATOMY AND PHYSIOLOGY OF FOLIOSE OR OPERCULATE MOSSES, -Mosses appear to consist entirely of cellular texture, which varies much in density, ancl in the form of the cells in different species, and even in different parts of the same species. In the stems and nerves of the leaves, the cells are narrow and elongated, from the effect of pressure. In many instances, the compression and elongation of the cells takes place chiefly at the circumference of the stem ; while those in the centre preserve very nearly their original hexagonal, penta gonal, or other, and frequently more complicated form ; indicating that in mosses, as in palms, vegetation is most active in the ccntre of the trunk ; while, from the ready and abundant ramification of a large proportion of species, this family has some analogy., in external aspect, to the dicotyledoneous vegetables. The elon gated cells have been described by Hedwig, the first of scologists, as straight tubes, analogous to those figur ed by Grew and Malpighi, as a constituent part of the larger plants, and as forming, in particular, a great part of the wood of ligneous dycotyledons. But in thc larger plants, these supposed tubes are now generally admitted to be merely condensed cellular substance; and in mosses, a gradation may be traced from the roundish, or angular and nearly equal-sided cell, to the tubiform appearance produced by elongation from pres sure. Hedwig concluded, from analogy, that spiral tubes exist in mosses, and adduced the disengagement of globules of air, about the size of moss seeds, from dissected portions of the stem, while he was examining them under a microscope, and from the dry calyptra when placed in water, as proofs of their existence. But Ile admits that lie had nevor been able to detect them by the knife and microscope ; and his hypothesis, that pollen is formed chiefly hy the agency of the spiral vessels, perhaps predisposed him to admit their exist ence upon slighter grounds than he might otherwise have considered necessary. The light which the re searches of that distinguished investigator have diffused over the structure and economy of mosses, entitle even his opinions to great respect : and Bridel, without adduc ing any new fact, considers the existence of the vessels in question to be established; thinks that they form tlie chief part of the meshes that divide what are usually termed the cells of the leaves; and doubts whether " in: these meshes the vessels form a single stratum only., or several strata superimposed, as in the leaves of the apple and orange." By means of these vessels, which he thinks traverse the whole structure of a moss, and hy them alone, arc we enabled to explain the transformation of a disciferous into a capsuliferous plant. But he does not show, in what manner these vessels would assist us in the solution of this difficulty. We are unable to see how it can be in any degree affected by the question about the presence or absence of spiral vessels, and think that it can be solved only by considering species which had been reckoned dioecious, to be really monoecious.
We distrust conclusions drawn from analogy, when the substances compared have so many points of dis crepancy, as musci and cotyledoncous plants. The
structure of the ridges that form the partitions between the cells, and of the slightly elevactd lines that cross the cells in different directions, is at nesent altogether unknown. It may consist of a conc>:..ries of extremely minute tubes; analogy perhaps favours that supposition; and we recommend the inquiry, as one of no mean inte rest, to the vegetable anatomist, and to botanists in general.
In the flat part of the leaves, the cells are in general less compressed than in the stems and nerves, yet even in the leaves they vary exceedingly in form in different species, and sometimes not a little in the same species, at different periods of growth. Very frequently bars, much more slender than the parietes of the cells, tra verse the cells in different directions, but chiefly in the direction of their narrowest diameter. These are very conspicuous in the genus Sphagnum, in which the cells are of a very peculiar form; and they are more or less visible, crossing the cells of most mosses. In Bookeria lucens the cells are of a rhomboidal form, the diameter between the angles pointing from the base to the apex of the leaf, being about twice as long as the transverse one. In Diphysicurn foliosum the cells appear some what like small irregluar openings in a very dense tex ture. And almost every moss has something peculiar in the form of its cells.
No pores have hitherto been traced on the surface of any moss ; and neither pores, nor any other means of communication, has been traced in the interior between the cells. Yet it is certain that they. are extremely per meable, and that they imbibe water with grcat avidity, not merely when in a state of active vegetation, but af ter they have been preserved dry for several years. A dried moss may thus, after having been preserved for any number of years, at any time be restored to its ori ginal verdure, and to the exact appearance which it had when growing, by simple immersion for a few mi nutes in water. There is, however, one case of excep tion. lf, in the original drying, great pressure, or the smoothing iron has been used, for the purpose of mak ing very showy specimens, then the original form can never he regained. Of course, if one set of these fine specimens be kept for show, there should be others, less artificially prepared, for use. It is remarkable, tlrat a moss which has been, from drought, quite arid, and in a state of torpor for several munths, or even for years, will, in many instances at least, on the re-appli cation of moisture, grow as vigorously as before the commencement of the torpidity. But mosses that have been deprived of litality by heat, or by whatever other means, imbibe moisture when dry, as rapidly as mosses merely torpid. It appears, then, that this quality of ab sorption in them is not dependent, or at least not always dependent, on the vital principle. May it not, then, be, at least in the dead moss, the result of a chemical affinity between water, and that modification of vegetable matter of which a moss is composed ? In regard to duration, mosses may be divided into an nual, biennial, and perennial.
The particular parts of mosses may be divided into conservative and reproductive organs.