292 



PLANT LIFE. 



fertilized. In these plants, therefore, we return to a con- 

 dition which is scarcely an alternation of sexual and spore- 

 producing phases, because the > 

 sexual phase is nearly obliterated 

 by reduction. 



395. Relative size of gameto- 

 phyte and sporophyte. --The ac- 

 companying diagram (fig. 335) may 

 roughly illustrate the history of 



f 



d 



c 



a 



FIG. 334. 



FIG. 335. 



FIG. 334. End of megaspore of Polygonum divaricatum. e, egg; s, s, synergi- 

 dae, probably sterile eggs. Below e the nucleus from whose divisions arise the cells 

 of the belated gametophyte. Magnified 540 diam. After Strasburger. 



FIG 335 Diagram representing the reduction of gametophyte and increase in sporo- 

 phyte from lower to higher plants, a, green algae; />, red algs ; c, liverworts ; d, 

 mosses; e, ferns;./", club-mosses; g, gymnosperms ; Ji, angiosperms. Original. 



development of these phases in the vegetable kingdom. 



The gametophyte phase is represented by the dotted area. 

 It has its greatest development in the lower algce and fungi, 

 where it constitutes the whole, diminishes at first slowly and 

 then rapidly. After the fernworts are passed it constitutes a 

 relatively inconsiderable part of the plant and almost disap- 

 pears among angiosperms. Of the sporophyte, represented 

 by the white area, the reverse is true. The lines crossing 

 the diagram at various levels show by their length in the 

 white and black areas the relative importance of the two 

 phases in the groups indicated. 



