ANTHER, POLLEN AND POLLEN TUBES 347 



D 



FIG. 58. Development of pollen (microspores) . A, cross-section of 

 anther showing four pollen sacs (microsporangia), one full of 

 pollen grains (microspores) ; also fibrous layer of wall and vascular 

 bundle. B, cross section of opened anther, with the walls of 

 the pollen sacs turned back. The dotted lines show their original 

 position and the arrows the direction of movement when they 

 break open. C, pollen grain with nucleus (right) and " genera- 

 tion cell," which represents the " male prothallus " (left). D, 

 germination of pollen grain. The nucleus has entered the tube 

 and is followed by the " generative cell." E, growing apex of 

 pollen tube with nucleus and two male gametes into which the 

 generative cell has divided. F, part of stigma with germinating 

 pollen grains, their tubes pushing down between the loose stig- 

 matic cells. 



