47 



No: 8. Another leaf on the fame Vranch pave the following results : - 



No. 9. A third leaf on the same branch gave results as follows : 



It will be noted that these measurements prove the growth of these 

 shot-holes to have been concomitant with the growth of the leaves. 

 In hardly any of the cases cited did the shot-holes appear as the result of 

 a piece of the leaf falling away as is often the case when the holes result 

 from the attacks of fungi. As the most careful examination failed 

 to reveal any trace of fungus growth in the tissues at the margin of 

 these holes, and as cultures made from these tissues failed to show 

 any adequate cause for their appearance, I concluded that my suspicion 

 as to their cause, namely, the small form belonging to the Thripsidse, 

 was fully justified. I am quite familiar with the production of shot- 

 holes through the agency of various species of fungi, but careful 

 search continued for a long time among the leaves of the trees 

 experimented on did not result in finding more than a very few cases 

 of holes due to this cause. 



We are driven to the conclusion that the " shot-hole " is a function 

 of the apricot leaf (no doubt the phenomenon is found in other genera) 

 and not of any particular disease. When irritated mechanically, or 

 attacked by a fungus disease, the tissues of the leaf act in this way, 

 no doubt in self defence. Though the leaf yield readily at the point 

 of attack it immediately sets up another line of defence, and this 

 consists of a new growth of tissue on all sides of the attacked part, 

 with the result that a hole is formed. 



The observations on the shot-holes of the apricot having been 

 interrupted in 1901, an attempt was made to continue them in 1902. 

 The season proved, however, to be different from the previous one, 

 and there was no reappearance of the larval form noted in connection 

 with shot-hole the previous season, and in conformity with this there 

 was very much less shot-hole on the trees that had harboured these 

 insects the previous season. After careful search at various times 

 during the spring had failed to bring these particular forms to light, 

 it was determined to transfer other species of Thripsidse to apricot buds 

 in order to see whether they would consent to remain there, the 



