274 



STRUCTURE OF MOSSES 



In the Mosses there is a definite stem, bearing three or more 

 rows of alternate sessile leaves. The plants either have a pros- 

 trate habit (e.g. Hypnum, Fig. 150, C), like that of most leafy 

 Liverworts, or grow erect, as in the Hair Mosses (Polytrichum, 

 Fig. 150, A, Fimaria, etc.). The lower part of the stem, which 

 is buried in the soil, forms a kind of rhizome bearing numerous 

 rhizoids, and sometimes small scales as well. The rhizoids, 



which may also 

 develop from the 

 part of the stem 

 just above the 

 soil, are out- 

 growths of the 

 superficial cells, 

 but differ from 

 those of Liver- 

 worts in being 

 multicellular and 

 branched ; they 

 usually have 



B HP ^Kl^ brown mem- 

 branes, and are 

 divided by 

 oblique septa, 

 j ust behind which 

 the branches 

 originate. 



The leaves of 

 Mosses are never 

 lobed, are at- 

 tached to the 



stem by a broad cushion-like base, and usually, except in the 

 region of the midrib, consist of a single layer of cells (Fig. 151, B). 

 The midrib (m.) is generally well differentiated, and its presence 

 forms a point of contrast with the leafy Liverworts. The branches 

 of the stem arise from below the leaves, and, in some of the 

 erect forms, are produced in such large numbers from the base 

 that the plants exhibit a densely tufted habit (e.g. Tortula, 

 Fig. 150, D). Many of the Bog-mosses (Sphagnum) are likewise 



FIG. 150. Various Mosses. A, Plant of Polytrichum, 

 bearing a sporogonium whose capsule is covered 

 by the calyptra (ca.}. B, Male plant of the 

 same, showing the antheridial head (a.}. C, 

 Hypnum, with sporogonium. D, Tortula 

 muralis. E, Male plant of Mnium, with an- 

 theridial head (a.}. 



