376 Insects and Potato Foliage 



These figures point, not very decisively, to the fly selecting for 

 egg-laying those plants with more leaves and more perfect ones; this 

 may mean (1) the fly prefers itself to repose on such foliage, (2) it prefers 

 to feed on such foliage, or (3) it definitely selects such foliage for egg- 

 laying on. On this point we can only say that there is a fair concurrence 

 of plants on which flies were found as well as eggs : that is that the plants 

 on which the flies sit and feed are also those on which they lay eggs (see 

 Series I — III). It is noteworthy that there is very much less scale on the 

 far smaller plants of Series IV than of Series I — III, though they were 

 throughout kept together; there is no plant in Series IV which in 

 Series I — III would have been marked as more than "scale moderate." 

 This may be due to the Series I — III plants being in higher pots and so 

 nearer the light or to their greater amount of foliage. 



It seems to be quite clear that there is a definite selection of plants 

 by the Aleurodes which may be connected partly with foliage but must 

 also depend upon some other character that we cannot determine. 



Afhis. Figs. 6, 7. 



No. 3. Four pots on soil under bell-jar placed on the soil. 



22. 3. 12. Placed twelve Aphides on each plant. These were of varied size, 

 including in each case two winged forms, and were taken from potato plants growing 

 in pots. 



26. 3. 12. Intumescences observed in the plants. 



1. 4. 12. Some leaves with discoloured veins. 



2. 4. 12. The Aphides were counted, being 43, 14, G, 16 respectively on the four 

 plants. 



5. 5. 12. One Aphis found on each plant. 



No. 4. Four pots under a bell-jar which is raised on inverted pots leaving a space 

 between the jar and the soil. Put in Aphides from the potato plant on 22. 3. 12. 

 1. 4. 12. The Aphides total 97, 40, 19, 54 on the respective plants. 

 Sorrie leaves with discoloured veins. 



5. 5. 12. A heavy infestation, the most Aphides on the lower surface of the lowest 

 leaves. The symptoms noted are: 



yellowing of the leaf generally; 



the veins on the lower surface become dark coloured ; 



the leaf tips and margins become brown, dry and brittle; 



the leaf eventually falls off. 



No. 5. 22. 3. 12. Four pots uncovered, each infested with 12 Aphides from a 

 potato plant. 



1. 4. 12. Several leaves with discoloured veins in all the plants. 



2. 4. 12. Aphides on plants number 46, 89, 108, 103 respectively. 



