io6 



GEORGE O. SHINJI. 



some idea of the amount of the wing-developing substances to be 

 effective in the development of the wing-buds, I instituted a 

 series of experiments. In these experiments, the solutions of the 

 magnesium sulphate, of various strengths, were poured directly 

 into a series of tumblers, in each of which a rose twig, bearing a 

 viviparous female, had been placed. 



TABLE IV. 



As will be seen from the table, I have been unable as yet to 

 reach the lowest strength at which the majority of the aphids 

 born on the twig would remain apterous. The table, however, 

 suggests that this minimum amount may lie beyond the strength 

 of an w/iooo solution. 



It may also be added here that the susceptibility to the chemi- 

 cals varies greatly with the species. Euceraphis betulce on the 

 birch tree growing on a sunny soil rarely or never produces ap- 

 terous forms, while a considerable number of Calaphis betu- 

 lacolens infesting the same host become winged. Macrosiphum 

 rosce also produce alate forms even on a relatively younger shoot, 

 but it is utterly impossible to raise winged Myzus persicce on a 

 similar host without the application of a wing-developing sub- 

 stance. 



VI. ON THE PHYSICAL FACTORS. 



i. Temperature. No special experiment for determining the 

 effect of temperature upon the development of the wings has 



