A. S. IIoRNE AND H. M. Lbfroy 377 



5. 5. 12. Three plants very heavily infested, one not. Of the infested ones, one 

 is withering, tlie leave.s Hmp, yellow, curling and browning at the tips, the veiils 

 dark; two have the leaves yellow, the veins dark, the tips brown. The plant now 

 fi'ee had the veins heavily dark, the leaves browning off from the tip. 



Since the plants of No. 5 were not confined, they became infested with 

 Aleurodes which was present in the greenhouse. The flies were con- 

 tinually removed to the extent that scale was present on only one plant 

 on April 19. 



A comparison with the controls shows that these symptoms were 

 undoubtedly due to Aphis. The plant under Cloche 7, control to 

 Aphis 3 (plant enclosed), did not develop discoloured veins (Fig. 8), 

 either on the leaves present at the time of the infestation or on the 

 leaves newly formed whilst under the cloche. The plants under Cloche 6, 

 control to Aphis 4, were with difficulty kept free. On April 2, 106 

 were removed, 48, 8, 40 and 12 respectively on the four plants, and the 

 veins of some leaves on the third and fourth plants were slightly dis- 

 coloured. The plants under Cloche 8, control to Cloche 5, were not 

 enclosed and hence exposed to repeated infestation. The Aphides were 

 frequently removed, 53 were removed on April 2 and the veins were 

 not discoloured, but soon a relative difference only could be observed 

 between the infested and control plants and the two sets soon became 

 equally and heavily infested. 



From the above results it will be seen that the earliest symptoms due 

 to Aphis show themselves on the leaves, the midrib and veins of which 

 become brown, and that these symptoms appear, irrespective of the 

 conditions under which the infested plants were placed, within ten days 

 from the date of infestation. 



The further progress of the infestation and the development of 

 later symptoms were, however, influenced by the conditions under 

 which the plants and Aphides were kept. On April 1, the distribution 

 of Aphides was as follows : Cloche 3, 79 ; Cloche 4, 210 ; Cloche 5, 346 ; 

 a result showing that the Aphides multiplied most on the plants not 

 confined, least on the plants entirely enclosed. In fact they gradually 

 decreased in number on the enclosed plants until on May 5th only four 

 remained. 



The symptoms rapidly increased on the plants not enclosed, the 

 leaves becoming yellow, the veins dark brown, and the leaf tip curled, 

 brown and dead. 



