42 Damage to Plant Tissue from Capsid Buys 



In the case of the apple fruit these dead cells present a dark red or 

 brown appearance owing to the formation of a tannin which gives a 

 black coloration with ferrous sulphate. Microtome sections of portions 

 of apple leaf injured by P. rugicollis show a mass of dead cells filled with 

 a red granular material, the epidermis dying after the mesophyll, this 

 confirms Petherbridge and Husain(2). When P. rugicollis feeds on Willow 

 a clear space is produced round each puncture so that if damaged by 

 several punctures the leaf becomes transparent and dies. Sections of 

 such a leaf show that the cells are killed and filled with a clear substance 

 very similar in appearance to that found in the cells of the apple, so that 

 the reaction appears identical with that produced in the apple, with the 

 exception of the colour reaction. The production of the red-brown 

 pigment is merely a death phenomenon of the apple cells and is no 

 special reaction to the Capsid ; apple leaves if held in chloroform vapour 

 produce the same red pigment. 



We come now to consider the possible explanations of this damage. 

 These seem to be three : 



Firstly, a purely mechanical injury caused by the laceration of the 

 tissues by the stylets in process of sucking. 



Secondly, the possibility of the bug acting as a "carrier" of bacteria 

 and injecting them into the plant along with the salivary juices and so 

 setting up a pathological state. An interesting parallel to this is found 

 in the case of the Beet Leaf hopper which carries the germs of beet 

 curly top (Stahl and Carsner(5)). 



Thirdly, the injection of some secretion, either from the salivary 

 glands, which is the more probable, or a regurgitation from the stomach 

 which has a virulent toxic effect on the tissue. These three theories seem 

 to cover the only possible explanations of the damage. As has been 

 mentioned already, the formation of the red brown pigment is a death 

 phenomenon of the apple and it is possible by means of laceration with 

 a sterile needle to produce a small brown spot similar in appearance to 

 that produced by the Capsid but not approaching it in extent of the 

 injury. The following attempts were made with sterile needles of varying 

 fineness to reproduce the injury caused by the bugs. 



(1) Scratch on the surface of the leaf with a dry sterile needle. 



(2) Puncture with dry sterile needle. 



(3) Scratch through sterile water. 



(4) Puncture through sterile water. 



(5) Puncture with dry needle not penetrating the leaf. 



In each case only cells actually lacerated by the needles were killed, 



