Seed-Plants 121 



which land plants are subjected. These limitations 

 are probably due to the fact that the gametophyte of 

 the archegoniates is essentially a water plant. Even 

 the most perfect garnet ophytes, such as are found 

 in the higher liverworts and mosses, owing to their 

 failure to develop an adequate root system and ef- 

 ficient mechanical or supporting tissues, are unable 

 to attain any but the most modest dimensions. 

 Moreover, these plants are essentially amphibious, as 

 water is necessary to effect fertilization. 



In the ferns the development of the race centers in 

 the sporophyte or neutral generation. The sporo- 

 phyte, being the product of the fertilized ovum, is 

 equivalent to the zygote or sexually developed rest- 

 ing spore of the ancestral green algae from which the 

 mosses and ferns are descended. As the zygote of 

 these algae is usually adapted to survive drought, we 

 may say that the sporophyte has never been an 

 aquatic structure, but from its earliest beginning is 

 an organism fitted for terrestrial existence. It evi- 

 dently possesses a potentiality for development on 

 land that is not shared by the essentially aquatic 

 gametophyte. It might be said that nature, having 

 in the mosses exhausted her resources in the en- 

 deavor to transform the aquatic gametophyte into 

 a successful land plant, turned to the spore-bearing 

 generation as a more promising subject for experi- 

 mentation. In the ferns there is encountered, then, 

 for the first time, a sporophyte which possesses true 

 roots having sufficient capacity for water absorption 



