318 Scientific Proceedings^ Royal Dublin Society. 



infected plants were put into the warm green-house with the hope of 

 carrying on the agamic generations, and the interesting result shown in 

 fig. 3 has been obtained. After October had set in, there was a marlvcd 

 tendency to production of sexual forms, and the agamic forms in most cases 

 died out. 



However, in the case illustrated in fig. 3 a few agamic a. v. + + 

 developed, and these were isolated, and their offspring carefully watched. 

 In each succeeding generation large w. v. + + (winged sexuparae, + pro- 

 ducers) and winged $ $ were produced ; and in every case one or two 

 agamic a. v. + + also developed, which were isolated to carry on the next 

 generation. It was not possible to follow out the exact numbers of each 

 form produced, owing to the great number of pots and plants that would be 

 required ; but winged sexuparae were in the majority, with a comparatively 

 small number oi i $ . The agamic a. v. + ? , on the other hand, were usually 

 only one, two, or three in each of the later generations. 



The development period of these agamic individuals is somewhat longer 

 than that of the summer generations, and the numbers of offspring produced 

 considerably less. This may to some extent be due to low concentration of 

 the cell sap of the plants, owing to conditions of winter sunshine and reduced 

 assimilation. 



It will be seen that agamic and sexual forms in the same generations 

 were obtained on Euonymus. 



The females produced by the winged sexuparae grew well on Broad 

 Beans, and became larger than normal females ; but in no case were ova 

 laid, although on dissecting these females several large eggs were found 

 inside them. These + + in the experiments were not fertilized, owing to 

 the fact that the Aphids were removed from the plants as they became 

 adult. 



In one case ten oviparous + +, born on a Bean plant on 1st January, 

 1921, had not produced ova by 16th February, and by that time only two 

 + + were alive. When some of the females were dissected, they were found 

 to contain several large eggs. 



Sexual forms were produced when the Aphids were kept continuously 

 on Euonynms curopaeus, and also when they were kept continuously on 

 Beans. 



As referred to in a previous paper (1921), sexual forms have been 

 recorded in the field on Bumex, Sugar Beet, and Haricot Beans. It is 

 evident, therefore, that the food plant in itself does not determine the 

 appearance of the sexual forms. It is very interesting that sexual forms 

 appear on the primary or secondary host, showing that the distribution of 



