278 THE THEORY OF THE GENE 



under changed conditions. McPhee, who has also studied 

 the effect of exposure to light for different lengths of 

 time, has found that male plants may produce branches 

 with pistils, and vice versa ; but he points out that many 

 intersexual flowers also appear as well as many abnormal 

 flowers. He states "that the changes produced are in 

 many cases relatively minor ones and a sweeping conclu- 

 sion that genetic factors are in no way concerned with 

 sex in these species is not warranted at the present 

 time. ' ' 



The question as to whether there is an internal sex- 

 determining factor system — possibly chromosomal — in 

 hemp, is at present unanswered, and as yet we have only 

 an oral report by McPhee concerning the genetic evi- 

 dence, but this report is significant. If the normal female 

 hemp plant is homogametic (XX) and the male hetero- 

 gametic, then we may expect when a female is trans- 

 formed into a male (or more accurately produces func- 

 tional pollen) that all the pollen grains will be alike as to 

 their sex-determining properties, i.e., such a male is 

 homogametic. McPhee 's oral report 5 supports this view. 

 Conversely, if the male (XY) is transformed into a fe- 

 male, then two kinds of eggs are expected. This seems to 

 be realized. 



Correns had earlier reported somewhat similar results 

 in other plants but the data relating to the kinds of 

 gametes produced are not satisfactory. It is to be hoped 

 that evidence will soon be available that bears on this 

 question. Assuming, in the meantime, that there is an 

 internal mechanism for sex-determination in hemp (pos- 

 sibly of the XX-XY type), there is nothing revolutionary 

 in the discovery that sex reversal may take place through 

 environmental agencies, and there is certainly nothing 

 in these results that is, in principle, in contradiction to 



5 At the meeting of the Zoological Society, 1925. 



