MOSSES 249 



composed of a single layer of cells, and in many cases have 

 a midrib. The sporophyte is more or less elongated, 

 enlarged above into a spore-case (capsule) and does not 

 contain elaters. 



438. The tissues of the Mosses present a considerable 

 advance upon those of the Liverworts. In the stem 

 there is frequently a bundle of very narrow thin-walled 

 cells, which in some species become considerably thick- 

 ened. In a few cases there have been observed bundles 

 of thin-walled cells extending from the leaves to the 

 bundles in the stem. It cannot be doubted, then, that 

 the Mosses possess rudimentary fibro-vascular bundles. 

 As in liverworts, the tissues of mosses develop from 

 a single apical cell. Breathing-pores (stomata) re- 

 sembling those of the higher plants occur on the sporo- 

 phytes; they are not found upon the leaves or stems. 



439. Mosses, for the most part, grow upon moist 

 earth or rocks, or upon the trunks and branches of 

 trees; comparatively few are 



aquatic. They range in size from 



less than a millimeter to many 



centimeters in length, the most 



common height being from 2 to 4 



centimeters. They are all chlo- Fia . m. A moss (protonema 



rophyll-bearing plants, and are and leafy gametophyte). 



generally of a bright green color; occasionally, however, 



they are whitish or brownish. 



440. The reproduction of mosses is mainly sexual, 

 but often brood-masses are found resembling those of 

 liverworts. The sexual organs develop either upon the 

 ends of the main stems, within flower-like rosettes of 

 leaves, or on the ends of short branches in the axils of the 

 leaves. 



441. The antherids are club-shaped or globose struc- 



