WHAT A FLOWER IS 



175 



ing. It is very marked in ferns and mosses. In alga? 

 (including the seaweeds) the gametophyte makes the 

 "plant," as the non- botanist knows 

 it. There is a general tendency, in 

 the evolution of the vegetable kingdom, 

 for the gametophyte to lose its rela- 

 tive importance and for the sporophyte 

 to become larger and more highly de- 

 veloped. In the seed-bearing plants 

 the sporophyte generation is the only 

 one seen by the non -botanist. The 

 gametophyte stage is of short dura- 

 tion and the parts are small : it is 



Confined to the time 31 - Fertile and sterile fronds 

 i. v .L of the sensitive fern. 



of fertilization. 



324. The sporophyte of seed -plants, 

 or the "plant" as we know it, produces 

 spores one kind being called pollen- 

 grains and the other kind embryo-sacs. 

 The pollen -spores are borne in sporan- 

 gia, which are united into what are 

 called anthers. The embryo -sac, which contains the egg- 

 cell, is borne in a sporangium known as an ovule. A 

 gametophytic stage is present in 

 both pollen and embryo -sac: fer- 

 tilization takes place, and a sporo- 

 phyte arises. Soon this sporo- 

 phyte becomes dormant, and is 

 then known as an embryo. The 

 embryo is packed away within 

 tight -fitting coats, and the entire 



body is the Seed. When the COn- 312. Prothallus of a fern. Enlarged. 



ditions are right the seed grows, Arcnegonia at a > antheridia at 6 - 

 and the sporophyte grows into herb, bush, or tree/ The 

 utility of the alternation of generations is not understood. 



311. A sac-like indusium. 



