ANGIOSPERMS 329 



pistil is primarily an asexual reproductive structure, and later 

 is given the appearance of sexuality by the fact that the game- 

 tophytes develop within it instead of free from the sporophyll, 

 as is true in the pteridophytes. 



There is great reduction in both gametophytes. In gymno- 

 sperms there were more cells in the male gametophyte, and 

 in some gymnosperms ( Cycads) not only are true sperms pres- 

 ent, but in some cycads there may be several sperms. In 

 angiosperms there are but two male cells and one nutritive 

 cell in the male gametophyte. The female gametophyte of 

 gymnosperms, while inclosed in the ovule, is a compact tissue 

 that bears several to many archegonia. In angiosperms, at fer- 

 tilization time, the female gametophyte consists of but seven 

 cells. The tissue is not compact. There is but one egg, and 

 it is borne without an archegonium. Accompanying this great 

 reduction of the female gametophyte are the added phenomena 

 of double fertilization and the second period of gametophyte 

 growth resulting in endosperm formation. 



The ovules are inclosed within the sporophyll that bears 

 them. This necessitates a much more extensive growth of 

 pollen tubes in order that fertilization may be effected. The 

 pollen-tube habit is so well developed in angiosperms that in 

 some plants, whose styles are several Inches in length, fertili- 

 zation will have occurred within a few hours after pollination. 

 This is of especial interest when we recall (1) that in the 

 pine about thirteen months elapse after pollination before the 

 pollen tube grows through the ovule tip to the egg ; and 

 (2) that in angiosperms the pollen grains sometimes alight 

 at a distance from the egg that is hundreds of times greater 

 than in gymnosperms, and grow fast enough to make their 

 way to the egg within a few hours. 



Gymnosperms are ancient plants, and seed-forming processes 

 in them occur slowly. Angiosperms are recent plants, and seed 

 formation in them occurs often very rapidly and in enormous 

 quantity. The abundant and effective production of seed is 

 an important factor in the present success of the angiosperms. 



