Xl] POLLEN AND SPORES 99 



through one of the thin areas of the exine, its nucleus 

 passing into the tube (pollen-tube). The nucleus and 

 protoplasm of the generative cell follow suit, the cell- wall 

 between generative and vegetative cells disappearing, and 

 the former divides into two generative nuclei as it enters 

 the tube. 



The germinated pollen-grain now consists of the 

 nearly exhausted grain behind, and the delicate pollen- 

 tube with the protoplasm in it, carrying at its anterior 

 end the vegetative nucleus, followed by two generative 

 nuclei. 



It is one of these generative nuclei which is eventually 

 handed over to the egg-cell (oosphere) of the ovule to 

 fertilise it. 



These are the essentials of the process of germination 

 of the pollen-grain, and they show that it is a spore, and 

 a spore, moreover, in which there are structures and 

 phenomena which must arouse our curiosity as to their 

 explanation. We find that they represent structures and 

 phenomena, here reduced and condensed, which recapitu- 

 late events in the germination of spores in the Cryptogams. 



In preparation for the comprehension of these, how- 

 ever, the student must observe that not all pollen-grains 

 behave exactly as above in detail, though they do so in 

 principle. 



In some, for instance, the vegetative and generative 

 cells, though their nuclei are divided off from one another, 

 have no recognisable cell-wall developed between this is 

 the common rule in the higher flowering plants. In 

 others the first division of the nucleus and cytoplasm of 

 the grain results in the formation of a large vegetative 

 cell, as before, separated by a wall from a smaller cell ; 

 then succeeds division of the smaller of the cells, and 

 it is one of these last formed which becomes the cell 



72 



