SEXUAL REPRODUCTION. 



28l 



Chara. bear- 



ol" 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 



reduction of the male game- 

 tophyte, that is, to a sex 

 organ alone, almost all trace 

 of resemblance to a plant 

 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 

 exact homologue of the 

 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 alter the microspore has been caught by the 

 moist surface | fluid in the micropvle or on the stigma | pro- 



By this extreme Fig. 313.— A, part of a "leaf 



ing sexual organs. /\ leaf; p. undeveloped 

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

 branch, sc; the dark oval body is the ovary 

 containing the fertilized egg; ,v, five cortical 

 cells which have grown spirally around the 

 ovary proper and become adherent to it ; 

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

 tween which the sperm makes its way to the 

 egg; ,1. the spermary, showing four of the 

 s toothed plates of which its wall is composed, 

 and the center ot each to which on the inside 

 the handle cell is attached. Magnified 33 

 diam. /•'. longitudinal section through young 

 "node" of a "leaf " of ( lhara, showing origin 

 and young stage ot sexual organs. / and in 

 stand in the c omers ot the adjacent tnternodal 

 .ells; between them is the thin nodal cell 



from which arise ;< and the sexual organs .vX- 

 and ,1 ; br, cortical tells co 

 is the young ovary not yet overgrown by the 

 cortical cells at its side's. ,,. the spermary, 



shows four wall cells outside, from which 

 their handle cells have just been divided; 

 all too young to shew relative sizes or shapes. 

 Magnified 2 1" diam Alter Sat hs. 



