ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 315 



conspicuous cytoplasmic body in one antherozoid and its absence in 

 the other. The difference is brought about, not during chromosome 

 reduction, but in the final division in the microgametophyte, and 

 has no apparent parallel, so far as I know^ in the cytology of any 

 other dioecious seed plant. However, little or nothing is known 

 regarding the corresponding division in other dioecious plants. 



Correns' (1907) well-known experimental studies of sex inheri- 

 tance in Bryonia seemed to show the existence in B. dioica of male 

 gametes of two kinds with reference to sex potentialities. Correns, 

 as well as most of those who have attempted an explanation of his 

 results, has assumed that this involves the existence of two kinds of 

 pollen grains, so strong has seemed the probability that the segrega- 

 tion of any particular hereditary factors is brought about by the 

 reduction divisions. It is, however, quite possible to assume that, 

 so far as sex potentialities are concerned, the pollen grains of 

 Bryonia are alike, and that the segregation of sex potentialities 

 occurs in the division of the generative cell within the pollen grain 

 or pollen tube. This suggestion, though based only upon the ob- 

 scure phenomenon recorded for Ginkgo, is perhaps worth testing, 

 in view of the failure of all attempts to find other visible bases for 

 the separate inheritance of staminate and pistillate characters. 



Department of Botany, 



University of Wisconsin. 



Literature Cited. 



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