298 PRACTICAL COURSE IN BOTANY 
bearing somewhat the aspect of lichens, met with everywhere 
on wet rocks and banks around shady watercourses. The 
say 
Fie. 427.—A 
shoot of peat moss 
with ripe spore 
fruits, f, f. 
life. Their relationship to the next higher _ 
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 truiting 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 
near the thallophytes that 
it is not difficult to recog- 
nize them as connecting 
links in the same chain of 
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 
Fic. 428.— A com- 
mon fern (Polypo- 
dium vulgare). 
development, and the group is of especial interest on account 
of its relationship to the higher plants. One of its divisions, 
