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 
