372 Insects and Potato Foliage 



To plants placed under cloches resting on inverted 



To plants placed under cloches resting on the 



To plants not under cloches. 

 Pots placed in a vessel containing water, and a 

 cloche inverted over the whole so that the atmosphere remained con- 

 stantly saturated. 



The plants used for the infestations had been uniformly treated, and 

 we selected as far as possible plants of a similar character and equal 

 amount of growth. 



Ejfect on the plants of the conditions under which they were placed. 



The plants grown under the cloches soon differed from those not 

 covered at all and the difference was most marked in the case of the 

 plants grown in an enclosed atmosphere. In a constantly saturated 

 atmosphere the plants became larger but procumbent, and developed 

 larger but thinner leaves than the uncovered control (Fig. 1). The 

 plants under cloches resting on inverted pots were less changed. 



Several of the plants responded to the experimental conditions by 

 the development of intumescences on the leaves. This feature was 

 more marked in the case of the plants grown under cloches placed 

 directly on the soil. 



Red Spider. 



No. 2. Four pots, on soil, under a bell-jar raised on inverted pots. 

 22. 3. 12. Put in leaves of Rhynchosia with many red spider on; the leaves 

 laid between the pots so as not to touch the plants or shade them. 



5. 4. 12. Abundant red spider on the plants. The symptoms produced were: 



cessation of growth ; 



yellowing of the leaves; 



many minute discoloured spots, giving the leaf a speckled, brownish 

 appearance ; 



eventual drying and browning of the plants, which die. 

 No curUng was produced at any time. 



One of the plants was photographed on three occasions — April 5, 13 

 and 17 — to show the progress of the infestation. (See Figs. 2, 3, 4.) 

 The experiment was repeated, using leaves from the plants already killed 

 by red spider, with similar results. 



It was observed that the plants did not all succumb to the attack 

 at the same time although the chances of being infested were equal. 



