LIFE HISTORY OF A LIVERWORT 225 
206. Comparison with Mosses and Ferns. (a) The 
Gametophyte. The gametophytes of the various kinds of 
liverworts differ greatly among themselves, but on the 
whole they are more simply organized than those of the 
mosses, lacking especially the highly developed, leafy 
branches or gametophores. The moss-plant represents 
the highest degree of gametophytic organization known 
among land-plants, and the leafy branch is practically 
universal in that group. On the other hand, the vege- 
tative body of the liverworts is, in some forms, simpler 
than the prothallus of the fern, while in other forms it is 
much more complicated, becoming a leafy branch in the 
Jungermanniales, and bearing complex gametophores and 
other organs in the Marchantiales. But while it may be- 
come complex, its organization is always of a lower type 
than that of the moss-plant. The antheridia are much 
alike in both mosses and liverworts, and on the whole 
differ but little from that of the true ferns ; but the sperma- 
tozoids of the former are always biciliate, while those of 
the true ferns are always multiciliate. The archegonia 
of mosses and liverworts may or may not be stalked, but 
they are never stalked in the true ferns. With the ex- 
ception of Anthoceros they are never sunk beneath the 
surface in either mosses or liverworts, but in the ferns the 
venter is commonly sunk in the tissue of the prothallus. 
(b) The Sporophyte. The typical sporogonium or 
sporophyte of liverworts and mosses consists of a stalk 
or seta, with a foot at one end, imbedded in the tissue 
of the gametophyte, and a spore-case at the opposite 
end. There are, however, all degrees of variation of this 
type of structure. The stalk and foot may be entirely 
wanting, as in the simple sporophyte of Riccia; the stalk 
is 
