FROM ALGA TO FERN 365 



producing tissues. There must be a large amount of 

 chlorophyll-bearing tissue, ample provision for taking in 

 abundant water and minerals, and efficient channels for 

 conducting the raw materials and elaborated food from 

 one part of the plant to another. Moreover, the spore- 

 bearing parts need to be lifted into the air to insure the 

 most efficient distribution of the spores. These needs 

 are admirably met by the sporophyte with roots on one 

 end, green leaves on the other, and sporangia borne at 

 or very near the tips of the branches. 



A review, at this time, of the sporophytic phases of the 

 liverworts, mosses, and ferns will show how these sporo- 

 phytes gradually increase in complexity and importance, 

 from the simple condition in Riccia, with almost no sterile 

 tissue, through the sporogonium of the higher liverworts 

 and mosses, to the leafy sporophyte of the ferns. The 

 final step in the development of the sporophyte was the 

 differentiation of megasporophytes, bearing only mega- 

 spores, and microsporophytes, bearing only microspores. 



331. Decline of the Gametophyte. As the sporophyte 

 became more highly developed and the dry-land flora 

 more firmly established, the gametophytic phase became 

 less essential and less in evidence, until, in the ferns, 

 the sporophyte became the commonly recognized "plant," 

 and the very existence of the gametophytic phase was, for 

 a long time, not known. Reproduction by spores and 

 by other non-sexual means became entirely sufficient to 

 perpetuate the race. 



332. Classification. By a careful comparison of all 

 .kinds of plants, it has been recognized that certain ones 

 are very much alike in fundamental characteristics of 

 structure; they fall naturally into a group. Moreover it 



