THE YKLJ.OVV CLOVEH APHIS. 27 



GENERATION EXPERIMENTS. 



Eggs which were laid on the stems and leaves of red <lover plants 

 in the fall of 1012 were kept out of doors under natural conditions 

 throughout the winter, and these began to hatch during the latter 

 half of April, 1913. The young which were used to begin the con- 

 tinuous-generation experiments hatched April 22, and it is worthy of 

 note that this was almost a month after the eggs of Macrosiphum pisi, 

 kept under identical conditions, hatched this same year. This is all 

 the more unusual since tnfolii invariably produces the sexual forms 

 and deposits its eggs noticeably earlier in the fall than does pisi. 



The young stem-mother — the aphis hatching from the egg being 

 so called — which hatched April 22 and was jDlaced on a red clover 

 plant gave birth to her first young on May 4 and her last young on 

 May 30. In the first-born generation series, that is, taking the first 

 young of the first young in each new generation, 17 generations were 

 obtained, counting the oviparous generation as the last. On the 

 other hand, in the last-born generation series, beginning with the last 

 to be borne by the individual which hatched from the egg April 22 

 and following the series of the last born of each "last-born" genera- 

 tion, there were in all only 8 generations. In other words, there 

 was a maximum of 17 generations and a minimum of 8, from which 

 we may reckon that the approximate average number of yearly 

 generations is 12^ (Tables I and II). 



