CHAPTER XXV. 



MOSSES (MUSCI). 



513. We are now ready to take up the more careful study of 

 the moss plant. There are a great many kinds of mosses, and 

 they differ greatly from each other in the finer details of struc- 

 ture. Yet there are certain general resemblances which make it 

 convenient to take for study almost any one of the common 

 species in a neighborhood, which forms abundant fruit. Some, 

 however, are more suited to a first study than others. (Polytri- 

 chum and funaria are good mosses to study.) 



514. Mnium. We will select here the plant shown in fig. 280. 

 This is known as a mnium (M. affine), and one or another of the 

 species of mnium can be obtained without much difficulty. 

 The mosses, as we have already learned, possess an axis 

 (stem) and leaf-like expansions^ so that they are leafy-stemmed 

 plants also. Certain of the branches of the mnium stand upright, 

 or nearly so, and the leaves are all of the same size at any given 

 point on the stem, as seen in the figure. There are three rows 

 of these leaves, and this is true of most of the mosses. 



515. The mnium plants usually form quite extensive and pretty* 

 mats of green in shady moist woods or ravines. Here and there 

 among the erect stems are prostrate ones, with two rows of promi- 

 nent leaves so arranged that it reminds one of some of the leafy- 

 stemmed liverworts. If we examine some of the leaves of the 

 mnium we see that the greater part of the leaf consists of a 

 single layer of green cells, just as is the case in the leafy -stemmed 

 liverworts. But along the middle line is a thicker layer, so that 

 it forme a distinct midrib. This ir characteristic of the leaves 



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