78 



ELEMENTARY STUDIES IN BOTANY 



The distinguishing mark of a moss, therefore, is the 

 leafy gametophore. It is these leafy and usually branch- 

 ing gametophores that people in general think of as the 

 " moss plant," for they are the most conspicuous part of 

 it. It is evident that green tissue in the form of leaves on 

 a gametophore is in a much better position in reference to 

 air and sunlight than green tissue prostrate on some sub- 



FIG. 60. The filamentous body of a young moss plant : A, the filament starting from 

 the spore (s) ; B, the older filament, showing the branching habit, rhizoids (r), and 

 a bud (6) which is to develop a leafy gametophore. After MUELLER-THURGAU. 



stratum, as in the Liverworts. Since the leafy gameto- 

 phore is only a vertical branch from the prostrate body, it is 

 often called the leafy shoot. 



In most Mosses the prostrate (dorsiventral) body does 

 not develop like those of Liverworts, but instead of being 

 a flat sheet of cells, it is a green, branching filament, resem- 

 bling a green, filamentous Alga (Fig. 60). It is important to 

 know that when the liverwort body is developing it passes 

 through a filamentous stage before it becomes a sheet of cells. 

 This means that the filamentous body of the moss is not a 



