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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 
—A moss (protonema 
centimeters. They are all chlo- yr. 104. 
rophyll-bearing plants, and are  %"4 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- 
