100 MORPHOLOGY OF POLLEN [CH. XI 



whose nucleus passes into the tube, and there divides into 

 two generative nuclei. 



In these cases, which are especially characteristic of 

 Gymnosperms, we get important clues to the meaning 

 of the processes, for the two- or three-celled rudimentary 

 tissue is shown to be a reduced prothallus, one cell of 

 which represents an extremely reduced antheridium, the 

 divided nuclei of which can only represent the antherozoids. 

 In the higher flowering plants we cannot trace these 

 homologies in detail; the reduction has gone so far that 

 only one cell the smaller represents the reduced 

 antheridium, and its two generative nuclei the anthero- 

 zoids, the vegetative cell being all that there is to 

 represent the prothallus. 



