386 Insects and Potato Foliage 



2. The effect on the foHage tissue in each case is as follows: 

 {a) Red Spider. — Epidermal and sub-epidermal cells injured. 



(6) Aleurodes.— Conducting tissue tapped, not followed by vein 

 discoloration. 



(c) Aphis. — Conducting tissue tapped followed by vein discolor- 

 ation after nine or ten days. 



{d) Jassid. — Epidermis punctured, assimilatory tissue destroyed. 



(e) Capsid. — Tissue lacerated causing severance of the veins and 

 leaving ragged, irregular pits which become rapidly discoloured as do 

 the veins also within two days. 



3. The markings caused by Jassids and Capsids proved distinctive 

 and could be recognised as such for some time after the injury, but for 

 the safe recognition of Aphis injuries the association of typical markings 

 with Aphides or their remains is necessary. 



4. Evidence has been obtained that Aleurodes select plants. 



5. Definite symptoms due to Aphis, Jassid and Capsid, correlated 

 with the presence or remains of these insects, have been found in the 

 field crops in several districts in three consecutive seasons. During 

 and after periods of wet weather the original injuries, especially those 

 caused by Aphis and Capsid, frequently obtain secondary extension, 

 and the foliage is prematurely destroyed. 



6. From field observations Aphides appear to exhibit a preference 

 for certain varieties or races of potato, but the question of selection has 

 not been experimentally studied by us. 



