116 



PLANT STRUCTURES 



leaves. There are really three rows of leaves, but the third 

 is on the ventral side against the substratum, and is often 

 so much modified as not to look like the other leaves. In 

 consequence of this the Jungermannia forms are usually 

 called "leafy liverworts," to distinguish them from the 



FIG. 99. Two liverworts, both Jungermannia forms: to the left is Blasia, which re- 

 tains the thallus form but has lobed margins; to the right is Scapania, with dis- 

 tinct leaves and sporogonia (A). CALDWELL. 



other Liverworts, which are "thallose." They are also 

 often called " scale mosses," on account of their moss-like 

 appearance and their small scale-like leaves. 



The line may be distinguished, therefore, as one in 

 which the differentiation of the form of the gametophyte 

 is emphasized. Another distinguishing mark is that the 

 sporogonium has a prominent seta, and the capsule splits 

 down into four pieces (valves) when opening to discharge 

 the spores (Fig. 100, C). 



71. Anthoceros forms. This line contains comparatively 

 few forms, but they are of great interest, as they are sup- 

 posed to represent forms which have given rise to the 



