BRYOPHYTES 



75 



swimming (Fig. 57). It is an interesting fact that the spores 

 became related promptly to air dispersal, but that the sperms 

 retained the water habit of swimming. This means that the 

 act of fertilization can take place only in the presence of 

 water, so that if a liverwort is kept from free water, fertiliza- 

 tion does not occur. It must be remembered, however, that 

 even " a film of dew " is sufficient water for the swimming of 

 such sperms. 



Among the Algae, the female sex-organ was called an 

 oogonium, but among the Liverworts and all higher plants 

 it is called an archegonium. It is so 

 constant in appearance that it is rec- 

 ognized easily in any group in which 

 it occurs (Fig. 58). The protective 

 jacket forms a flask with a more or 

 less slender neck, and in the body of 

 the flask the egg is formed. The two 

 regions of an archegonium, therefore, 

 are the neck, through which the sperms 

 pass to reach the egg, and the venter 

 (the body of the flask) in which the 

 egg lies. 



When the water conditions are favor- 

 able, the sperms swim to the archegonia, 

 enter the necks, reach the eggs, and 

 fuse with them, and the result is a fertilized egg (oospore) in 

 each archegonium. 



46. Alternation of generations. A most important fact 

 in connection with Liverworts remains to be told. Among 

 the ordinary Algse, the fertilized egg, just as the spore, 

 produces a plant like that from which it came, so that the 

 life-history formula ( 17, p. 24) is Pn2>o P. But when 

 the fertilized egg of a liverwort germinates, it produces 

 a very different kind of plant. This new kind of individual 

 is a spore-case, which in most Liverworts has a stalk, and the 



FIG. 58. Marchantia: an 

 archegonium, showing the 

 long neck, and the venter 

 containing the egg. 



