ginkgoale:s 



207 



becoming brown and forming a resistant beak tlial long persists as a 

 cap on the sac. The ]K)llen grains, carried well below the beak by 

 the deepening of the chamber, send out their tubes in every direction 

 into the adjacent nucellar tissue, but chiefly away from the embryo 



235 



236 



237 



2<»0 



239 



Figs. 235-240. — Ginkgo hiluha: the male gametophyte; fig. 235, pollen grain, 

 showing evanescent prothallial cell and persistent prothallial cell; the mitosis in the 

 antheridium initial will form the generative and tube cells; April 24; X500; fig. 236, 

 pollen at the shedding stage, with prothallial, generative, and tube cells; X500; fig. 237, 

 part of pollen tube July 10; X500; fig. 238, the nucleus of the generative cell has 

 divided, the stalk and tube nuclei lying side by side; July 11; X500; fig. 239, the body 

 cell has divided; blepharoplasts are faintlv visible; X120; fig. 240, the two sperms 

 produced l)y the body cell; September 11; X226. — .A.fter Hirase (16). 



sac, and often directly toward the beak. Into these young tubes the 

 tube nuclei pass, and remain there so long as the tube_] system 

 is developing. 



About the beginning of July, the tubes have penetrated the nucel- 

 lar tissue deeply and have branched freely, the tube nucleus remaining 

 where a tube begins to branch. This extensive system of branching 



