C. J. Bond 351 



PART III. 



The question now arises whether the factor, or factors, which 

 control sex segregation in the monoecious plant are the same as those 

 which determine sex in dioecious plants and in animals. 



In animals and dioecious plants segregation of the factors con- 

 trolling sex takes place among germ cells either before or during 

 fertilization, whereas in the Mowers of monoecious plants segregation 

 takes place among cells which present the external characters of somatic 

 cells although they no doubt retain germinal material capable not only 

 of forming new individual plants by bud formation, but also of acting 

 as the carriers of hereditary characters. 



But both processes depend essentially on qualitative cell division. 

 In one case this takes place in the meristematic cells of the plant stem 

 and results in maleness passing into the terminal and femaleness into 

 the lateral daughter cells, or vice versa ; in the other case it occurs 

 amongst male and female bearing gametes at an earlier stage of their 

 life history, probably at the period of maturation. 



The chief distinction between the two processes is one of time of 

 occurrence rather than one of kind. One affects the germ cell at or 

 before fertilization, the other affects the zygote which results from the 

 repeated division of this germ cell after fertilization. 



It seems clear that the association between the segregation of 

 primary and the segregation of secondary sex characters is less intimate 

 in plants than in animals. Both depend on qualitative cell division, 

 but the primary sex organs do not exercise such continuous control 

 over and are not so indispensable to the growth of the corresponding 

 secondary sex characters in plants, as in animals. In the higher 

 animals, unlike some invertebrates, a very elaborate system of inter- 

 dependence and control is present between those cell divisions which 

 represent primary maleness and femaleness and those metabolic pro- 

 cesses which underly the production of male and female secondary sex 

 characters. The functional activity of the latter is dependent on the 

 functional activity of the former, whereas in the case of the monoecious 

 plant the determination of the sex of the flower, and the number and 

 arrangement of its petals, although both may be primarily under the 

 control of a common genetic factor, are more or less independent 

 processes. 



Journ. of Gen. iv 23 



