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 archegonium 
on the underside of the archegonial head, thus forming the 
odspore. The odspore grows and produces an inconspicuous 
sporophyte, which in turn produces asexual spores.! 
255. General facts about ferns. The third great division of 
the plant kingdom is usually spoken of as the ferns (ptert- 
dophytes). The group includes other classes, two of which are 
Fic. 206. A common liverwort (Marchantia) 
{, an antheridial plant; B, an archegonial plant; rhizoids (rh) and midrib (m) 
of the leaf-like flattened body (2); capsules (c), in which vegetative reproductive 
buds are formed; the upright stalks (s) are antheridial (a) and archegonial (ar), 
the latter being distinguished by peculiar rays (7). 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. 
