Sex Dclcrniinuliofi 195 



sexes. A favorite subject for such cxpcriincnts is Cuuua- 

 bis, and many investigators have succeeded in a certain 

 amount of artificial manipulation of sex in this fonn. 

 ScHAFFNER (20) has gone so far as completely to reverse 

 the sex of given individuals by m()dif>'ing the cultural 

 conditions. He voices the belief of many other botanists 

 when he draws the following conclusions: 



''Sexuality is a state or condition not Mendelian in 

 nature, but related to functional activity of the plant 

 and profoundly influenced by cn\'ironment. Malcness 

 and femaleness in hemp are probably controlled by the 

 metabolic level of the cells, and sex reversal takes place 

 when the metabolic level is decidedly changed or dis- 

 turbed. Any tissue in its growth may be in a neutral 

 state of varying degrees of intensity, and during its 

 continued growth can pass from one state to the other 

 without any reference to chromosome segregation or 

 combination which are the ordinary causes of Mendel ian 

 phenomena." 



The situation might be clarified somewhat b\ the 

 following generaUzation. Not only are there relatively 

 fewer plants than animals in the unisexual condition, 

 but even in those plants that arc unisexual, this condition 

 is not so completely ''established" as in animals. 'J'iie 

 sex chromosome mechanism seems to operate only in 

 organisms where the purely unisexual condition prevails 

 and has prevailed for some time back in their i)hylo- 

 genetic history. Many of the dioecious angiosj)enns, 

 however, seem rather recently to have been deri\-e(l from 

 ancestors which have the two se.xes represented in the 

 same flower (or at least on the same plant). In these the 

 dioecious condition seems not to have been firmlv estab- 



