52 Biological Studies ry/Ai)his rumicis 



history of the aphids used was known and also the exact generation 

 with which the various plants were infected. Apterous viviparous ?$ 

 were used for the infections, as winged forms are often at first restless 

 on the plants, and it is difficult, when deaUng with large numbers, to 

 get a fair estimate of reproduction. 



The plants were all grown from seed (except Euonymusy, and were 

 kept covered with musHn bags throughout the experiments, to safe- 

 guard against outside infection. The aphids were transferred from one 

 plant to another by means of a fine camel hair brush. 



Unfortunately for the 1920 experiments, ova of Aphis rnmicis could 

 not be found, and the colonies in these experiments were started from 

 an early viviparous parthenogenetic generation found on Exonynnis 

 europaeus on the laboratory farm on May 10, 1920. This generation was 

 probably the second viviparous generation after the Fundatrix. In 

 future experiments however, it is hoped to breed all the aphids from 

 one egg and one Fundatrix. 



It will be seen that the figures obtained in 1920, in general, support 

 the results obtained in 1914. 



The plants used in any particular series have as far as practicable 

 been plants of the same age. They were grown in ten-inch pots and 

 kept covered with mushn bags throughout the experiments. Unmanured 

 soil, to which 10 per cent, of sand was added, was used. The plants were 

 kept in a large glass house specially designed mth large doors and 

 windows. The great variation in temperature is a source of difficulty, 

 since temperature is an important factor in affecting the development 

 period and the number of aphids produced in a definite period of time. 

 This has to some extent been overcome by arranging as far as possible 

 that infections in each series of experiments were carried out on the 

 same day. The temperature and humidity factors are thus relatively 

 the same for each series of experiments. The temperature (daily, max. 

 and min.) for the period June 25, 1920 to August 4, 1920 in the glass 

 house is shown in Text-fig. 1 below. 



Series A. Infections from Euonymus to Different Plants. 



(a) The aphids were reared throughout on Euonymus europaeus from 

 Fundatrices, and the following plants infected with winged migrants of 

 the 3rd v. gen. : broad beans, horse beans, poppies {Papaver rhoeas), peas, 

 rumex, dwarf French beans and Euonymus einopaeus. These plants 

 were "stock" plants for infections to other plants of the same kind. 



1 My thanks are due to Messrs Sutton & Sons who supplied the seeds used in these 

 experiments. 



