370 



STKUCTURE OF MOSSES. 



Fig. 180. 



detailed scrutiny of the practised 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 medul- 

 lary 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 pro- 

 longations pass into the leaves, so as to afford 

 them a sort of midrib. The Leaf usually con- 

 sists 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 struc- 

 ture, is commonly found on the Setce or 

 bristle-like footstalks bearing the fructifica- 

 tion, and sometimes on the midribs of the 

 leaves. The Leaf-cells of the Sphagnum (Bog- 

 moss) exhibit a very curious departure from 

 the ordinary type ; for instead of being small 

 and polygonal, they are large and elongated 

 (Fig. 181); they contain spiral fibres loosely 

 coiled 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-Animalcules that 

 make their habitation in these chambers. 

 Between 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 ' differen- 

 tiation.'* The Root-fibres of Mosses, like 

 those of Marchantia, consist of long tubular 

 cells of extreme transparence, within which 

 the protoplasm may frequently be seen to 

 circulate, as in the elongated cells of Chara ; 

 and according to Dr. Hicks ("Quart. Journ. Microsc. Science.," N.S., 

 Vol. ii., 1862, p. 96), it is not uncommon for portions of the 



* See Mr. H.'s very important Article on 'The Cell-Theory' in the 

 " British and Foreign Medico-Chirurgical Review," Yol. xii. (Oct. 1853), 

 pp. 306, 307. 



Elater and Spores 

 of Marchantia. 



