BRYOPHYTES 



291 



We shall learn, as indicated above, that this simple sporophyte 

 of the liverwort is the forerunner of the leafy green plant body 

 of the ferns and the seed plants like the mandrake and the bean. 



The sporophyte of Ricciocarpus is therefore a simple kind of 

 sporophyte plant, produced from the zygote, which grows as 

 a parasite on the mother plant, or gametophyte, and is devoted 

 wholly to the production of spores. 



Life history. In Fig. 161 the main stages in the life history 

 of Ricciocarpus and Vaucheria are represented by diagrammatic 

 figures to bring out the essential points of contrast between them. 



Sex Gametes Sporo- 

 Gametopliyte organs \ Zygote phyte Spore Gametophyte 



Gametophyte Sex "~T 



organs Gametes 



Gametophyte 



FIG. 161. Life history of Ricciocarpus and of Vaucheria, represented graphically 

 a, stages in the life history of Ricciocarpus ; b, stages in the life history of Vaucheria 



In the liverwort the gametophyte is bulkier and more highly 

 differentiated than in the alga, and is thus better able to meet the 

 aquatic or amphibious conditions under which it has to live. 



The reproductive organs, instead of being, as in the alga, 

 single-celled structures adapted to form the gametes, are com- 

 plex cellular organs, with an outer protective cell layer inclosing 

 the more delicate cells which form the gametes and aid in 

 fertilization. 



The zygote is formed in both the liverwort and the alga by 

 the union of the male and female gametes in fertilization, and 

 consists in each case of a single cell with a protective cell wall, 

 cytoplasm, and nucleus, like the zygote of Spirogyra. 



