SEXUAL REPRODUCTION. 



28l 



of the gametophyte and the others the spermary (fig. 316). 

 In angiosperms the vegetative part seems to have vanished 

 and the two cells which are formed constitute the spermary, 

 the smaller representing 

 the sperm cells and the 

 larger the wall cells (fig. 

 317; compare fig. 315). 

 Sometimes, indeed, the 

 smaller cell is only repre- 

 sented by a nucleus, no 

 partition wall being pres- 

 ent. Thus, the spermary 

 in all seed plants has almost 

 become a simple one again 

 by reduction from the com- 

 pound spermary of their 

 ancestors. By this extreme Fig. 

 reduction of the male game 



313. — A, part of a 



leaf " of Chara, bear- 

 sexual organs, b, leaf; /3, undeveloped 

 "leaflets"; /3', leaflet; 0", leaflets of the 

 branch, sc ; the dark oval body is the ovary 



tOphyte, that IS, tO a Sex containing the fertilized egg ; s, five cortical 



cells which have grown spirally around the 



Organ alone, almost all trace ovary proper and become adherent to it; 



they terminate in c, the five crown cells, be- 



Of resemblance tO a plant tween which the sperm makes its way to the 



egg; a, the spermary, showing four of the 

 8 toothed plates of which its wall is composed, 

 and the center of each to which on the inside 

 the handle cell is attached. Magnified 33 

 diam. B, longitudinal section through young 

 " node " of a " leaf " of Chara, showing origin 

 and young stage of sexual organs. I and iv 

 stand in the corners of the adjacent internodal 

 cells ; between them is the thin nodal cell 

 from which arise u and the sexual organs sk 

 and a ; br, cortical cells covering /, iv. 



the young ovary not yet overgrown by the 

 cortical cells at its sides, a, the spermary, 



has been lost, and it is diffi- 

 cult to think of the pollen- 

 grain (microspore) as pro- 

 ducing a real plant. This 

 male plant, though ex- 

 tremely small and simple 



even when mature, is the shows four wall cells outside, from which 



their handle cells have just been divided ; 



exact homologlie Of the all too young to show relative sizes or shapes. 



Magnified 240 diam. — After Sachs. 



larger male plant produced 



by the spores of the mosses, ferns, horsetails and selaginellas. 



386. Pollen tube. — The maturity of the male gametophyte 



is reached only after the microspore has been caught by the 



moist surface (fluid in the micropyle or on the stigma) pro- 



