TETRAPLOIDS 



111 



or the other pole bringing about reduction. Cleland has 

 recently described an end-to-end union of the chromo- 

 somes of another diploid species, Oenothera franciscana, 

 as they enter the maturation spindle (Fig. 66). Some of 



Fig. 66. 

 The maturation of the pollen cells in Oenothera franciscana. 



(After Cleland.) 



the earlier figures of Davis had also to some extent indi- 

 cated an end-to-end union. 



In other monoecious flowering plants tetraploids have 

 also been found in recent years. It is obvious why these 

 occurrences should be more frequent in monoecious spe- 

 cies than in species with separate sexes ; for, in the 



