SEXUAL VARIATION 109 



develop into male plants when the soil is poor in 

 nitrogen, or when the seeds are very near each other, 

 they yield female plants when nitrogen is abundant, 

 and the seeds somewhat distant. 



Yung's experiments on tadpoles had already been 

 performed by Born with similar results, and it seems 

 that in the human species, a change of climate is 

 often conducive to a larger production of females. 

 In Java, for instance, European or white children are 

 born in the proportion of five females against two ,' 

 males ; in Yucatan, in the proportion of eight / 

 females against two males. 



All these facts go to show that sexuality is in 

 great part determined by external factors, whatever 

 these may be, and that much variability is here 

 present. This variability may be readily seen in the 

 same species, under different conditions, and even 

 in the same individual. For instance, Carriere has 

 pointed out that variability is common in Ailanthus 

 glandulosa,%. well-known plant in which the distribution 

 of sexes is very inconstant. While some individuals 

 bear a large number of female flowers, many bear but 

 few, and it is a curious fact that they are all to be 

 found on the same branch, instead of being on different 

 branches, interspersed with male flowers. There 

 seems to be some special condition in one or more 

 branches which determines the production of female 



