44 Damage to Plant Tissue from Capsid Bugs 



Taking all these facts into consideration, it will be seen that mech- 

 anical injury alone is not sufficient to account for such serious damage. 



Turning now to the second possible explanation, that of injection of 

 bacteria with the salivary juices, the following experiments were made 

 to decide this point: 



Very thin microtome sections of the salivary glands of Plesiocoris 

 rugicollis and one or two other apple feeding bugs were cut in order to 

 verify if possible, the presence of bacteria in the glands and ducts; the 

 sections were stained with various bacterial stains, such as Victoria Blue, 

 Carbol Fuchsin, Gram's Stain etc., but in no case were there any indi- 

 cations of bacteria. Sections were also cut of the damaged portions of 

 apple and willow leaves and stained with various bacterial stains as 

 above, in order to trace bacteria in the cells. Although some of the cells 

 presented a slightly granular appearance, this was found to be due to 

 the presence of the tannin and no bacteria could be discovered. Apple 

 leaves badly damaged by P. rugicollis were then taken and ground up 

 with sterile sand in a mortar under sterile conditions with the addition 

 of a little sterile water, the resulting extract was allowed to stand and 

 the clear red fluid drawn off, it was then injected with a sterile hypo- 

 dermic syringe into undamaged apple and willow leaves. A solution of 

 damaged willow leaf was made under similar conditions and also injected 

 into apple and willow leaves. 



The inoculations made were as follows: 



(1) Inoculation of apple leaf with sterile water control. 



(2) Inoculation of apple leaf with extract of damaged apple leaf. 



(3) Inoculation of apple leaf with extract as in (2) but boiled. 



(4) Inoculation of apple leaf with a similar extract of willow leaves 

 damaged by the same insect. 



(5) Inoculation of apple leaf extract as in (4) but boiled. 



A certain amount of damage was produced in each case, very slightly 

 more marked in (2) and (4) than in the others. Five precisely similar 

 injections were then made into willow leaves, these gave negative results, 

 only such cells as actually came into contact with the hypodermic needle 

 apparently being affected. 



Bacterial cultures were then made from the damaged leaves as 

 follows. The leaves were ground up as before with sterile sand and 

 sterile water under sterile conditions and a drop of the resulting fluid 

 was added to 10 c.c. of sterile water and plated out on various media, 

 Turnip Agar + 4, Potato Mush Agar, Beef Agar, etc., after five days 

 many small round colonies were observed, these were plated out until 



