298 



PRACTICAL COURSE IN BOTANY 



bearing somewhat the aspect of lichens, met with everywhere 

 on wet rocks and banks around shady watercourses. The 

 name is a reminiscence of their former use 

 in medicine as a specific for diseases of the 

 liver, and not, as in the case of the liver leaf, 

 of a fancied resemblance to that organ. 



Mosses are one of the best defined of 

 botanical orders, and are easily recognized 

 by their slender, leafy fruiting stalks, grow- 

 ing usually in dense, spreading mats, and 

 presenting every appearance of a highly 

 organized structure, well differentiated into 

 root, stem, and leaves. 



The liverworts represent 

 the more primitive division 

 of the group, and in some 

 of their forms approach so 

 FIG. 427. A near the thallophytes that 



shoot of peat moss ft fe not difficult to TCCOg- 

 with ripe spore-. , . 



fruits, /, /. nize them as connecting 



links in the same chain of 

 life. Their relationship to the next higher 

 group is not clear, but while they represent 

 a more primitive stage of evolution than 

 the mosses, the development of the latter 

 has followed a course divergent from the 

 main line of evolutionary progress. 



335. III. Pteridophytes, or fern plants, are 

 classed roughly in the three divisions of 

 ferns, horsetails, and club mosses. They 

 differ greatly in structure, but all possess a 

 vascular system, and a well-organized struc- 

 ture of root, stem, and leaves. They rank 

 next to the spermatophytes in the order of 

 development, and the group is of especial interest on account 

 of its relationship to the higher plants. One of its divisions, 



FIG. 428. A com- 

 mon fern (Polypo- 



