310 Scientific Proceedings, Royal Dublin Society. 



14. 10. 20. Plant shedding its leaves ; a. v. ° ° , w. v. ° ? , ^J <? and sexual 

 $ $ present ; ova laid. 



Euonymus Eg. — 14. 9. 20. Infected with 15 w. v. 5 $ from Beans B4. 

 This plant has a lot of young growth. 14. 10. 20. Many aphids present ; 

 (J ^ and sexual 5 + present. 



Euonymus E,o — 11. 10. 20. Infected with 10 w. v. ^ + fi""™ Beans B5. 

 14. 10. 20. Only two winged forms producing on the plant. 30. 10. 20. Off- 

 spring now adult, all sexual 5 ° , 16 in number. 



Euonymus Eu. — :(Kept in warm greenhouse.) 24. 11. 20. Infected with 

 one w. v. 5 from Beans B,. 9. 12. 20. Offspring all oviparous 5 + , 24 in 

 number, some adult. 26. 12. 20. Ovip. % ? , large size ; no ova produced. 



Euonymus E^j. — 25. 2. 21. Infected with one w. v. ? (sexupara) from 

 Beans Bis. 12. 3. 21. Only oviparous 5 $ produced, some nearly adult. 

 12. 4. 21. All the oviparous + + alive, have distended abdomen ; no ova 

 laid. Ova in the bodies, but females not fertilized. 



II. — General Discussion. 



A. — Aiypearance of Winged Forms. 



It was almost universally held by the earlier investigators who studied the 

 biology of Aphids that poor sap conditions obtaining in plants resulted in 

 the production of winged forms. Later investigations indicated that tempera- 

 ture and humidity may also be important factors. 



The results obtained by these earlier workers have been so often reviewed 

 in the literature on Aphids that it seems unnecessary to review them again. 



Starting therefore with Mordwilko (1907-1909), who in his extensive 

 observations on the biology of Aphids gives a general idea of the views 

 obtaining at that time, we see that food conditions, probably correlated with 

 temperature, were accepted as the important factors. 



Investigations during the next few years on the life cycle of Aphids from 

 the cytological aspect lead one to the view that, although external factors 

 may have some influence on the production of winged forms, tliere is in 

 all probability some internal inherent mechanism at work which is the 

 important factor. 



Later results obtained from breeding experiments, notably by Klodnitzki 

 (1912), Baker and Turner (1916), and Matheson (1919), in which winged 

 forms were obtained in many of the parthenogenetic generations, would seem 

 to support this view. The situation at present is, however, by no means 

 clear, and external influences, especially of food and temperature, would 

 appear to be very important factors in the results obtained by some recent 

 workers, notably Ewing (1916) and Shinji (1918). In discussing this 



