348 MICROSCOPIC STRUCTURE OF HIGHER CRTPTOGAMIA. 



themselves (Fig. 132), tearing apart the cell-membrane ; and they 

 do this suddenly, so as to jerk forth the spores which may be 

 adherent to their coils, and thus to assist in their dispersion. 

 The spores, when subjected to moisture, with a moderate amount 

 of light and warmth, develope themselves into little collections 

 of cells, which gradually assume the form of a flattened frond ; 

 and thus the species is very extensively multiplied, every one of 

 the mass of spores, which is the product of a single germ-cell, 

 being capable of giving origin to an independent individual. 



216. The tribe of Mosses is as remarkable from the 

 Fro. 132. delicacy and minuteness of all the plants composing it, 

 as other orders of the Vegetable Kingdom are for the 

 majesty of their forms, the richness of their foliage, or 

 the splendor of their blossoms. There is not one of 

 this little tribe, whose external organs do not serve as 

 beautiful objects, when viewed with low powers of the 

 Microscope ; while their more concealed wonders are 

 admirably fitted for the detailed scrutiny of the prac- 

 tised observer. The Mosses always possess a distinct 

 axis of growth, commonly more or less erect, on which 

 the minute and delicately formed leaves are arranged 

 with great regularity. The stem shows some indication 

 of the separation of a cortical or bark-like portion, from 

 the medullary or pith-like, by the intervention of a circle 

 of bundles of elongated cells, which seem to prefigure 

 the woody portion of the stem of higher plants, and 

 from which prolongations pass into the leaves, so as to 

 aflbrd them a sort of midrib. The leaf usually consists 

 of either a single or a double layer of cells, having 

 flattened sides by which they adhere one to another; 

 they rarely present any distinct epidermic layer; but 

 such a layer, perforated by stomata of simple structure, 

 is commonly found on the setce or bristle-like footstalks 

 bearing the fructification, and sometimes on the midribs 

 of the leaves. The leaf-cells of the Sphagnum (bog 

 moss) exhibit a very curious departure from the ordi- 

 nary type ; for instead of being small and polygonal, 

 sporeJ'of" tliey are large and elongated (Fig. 133) ; they contain 

 Marchantia. Spiral fibrcs looscly coilcd in their interior; and their 

 membranous walls have large rounded apertures, by 

 which their cavities freely communicate with one another, as is 

 sometimes curiously evidenced by the passage of Wheel Ani- 

 malcules, that make their habitation in these chambers. Be- 

 tween these coarsely spiral cells, are some thick-walled narrow 

 elongated cells, which give to the leaf its firmness; these, in the 

 very young leaf (as Mr. Huxley has pointed out), do not differ 

 much in appearance from the others ; the peculiarities of both 

 being evolved by a gradual process of " difi^erentiation." The 

 chief interest of the Mosses, however, to the Microscopist, lies 



