LIFE HISTORY OF A LIVERWORT 225 



205. 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 hiciliate, 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, bi:^t in the ferns the 

 venter is commonly sunk in the tissue of the prothallus. 



(h) 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 



