MOSSES, LIVERWORTS, AND FERNS 



269 



formed. Special antheridial heads produce antheridia and 

 sperms, and special archegonial heads produce archegonia and 

 eggs. The sperm unites with the egg within the archegonmm 

 on the underside of the archegonial head, thus forming the 

 oospore. The oospore grows and produces an inconspicuous 

 sporophyte, which in turn produces asexual spores. 1 



255. General facts about ferns. The third great division of 

 the plant kingdom is usually spoken of as the ferns {pteri- 

 dophytes). The group includes other classes, two of which are 



rh ' B ' rh 



FIG. 206. A common liverwort (Marchantia) 



A, an antheridial plant ; B, an archegonial plant ; rhizoids (rh) and midrib (m) 

 of the leaf-like flattened body (7) ; capsules (c), injytrich yggfttative rp.prodnp-tivft 

 buds are-fewned; the upright stalks (*) are antheridial (a) and archegonial (ar), 

 the latter being distinguished by peculiar rays (r) . Slightly more than natural size 



the scouring rushes, or horsetails, and the club mosses. There 

 is good evidence that ferns were formerly more numerous upon 

 the earth than they now are, and some of the early ferns were 

 of much larger size than those that now exist. During the times 

 when coal was being formed most abundantly, ferns and their 

 near relatives composed a conspicuous part of the flora. Some 



1 Discussion of the different kinds of liverworts and the details of liver- 

 wort reproduction are not important for most elementary classes. In special 

 cases where it is deemed best to make further study, see Bergen and Davis, 

 Principles of Botany. 



