49 



The apricot trees upon which the shot-holes were produced by 

 thrips in 1901 also harboured aphides, and it naturally suggested itself 

 that they might be responsible for some of the holes in the leaves. 

 A colony of several score were established at the end of an apricot 

 branch, and were isolated by means of a cotton-wool barrier tied round 

 the branch. The bud was examined to make sure that there were no 

 thrips in it. Ants were kept away by the cotton wool barrier at 

 least for the most part ; for in spite of the obstacle a few ants, with a 

 persistency worthy of a great cause, and after an arduous struggle, did 

 make their way to the aphides. This happened so seldom that it 

 may be said that this particular twig, at least in the part beyond 

 the cotton -wool, was inhabited by aphides alone. The aphides 

 located themselves principally on the stem and petioles and veins of 

 the larger leaves. They never made their way into the narrow 

 recesses of the inmost bud. The branch suffered severely from the 

 infestation, and it may be here added died the next season, no 

 doubt from this cause alone. Its leaves did not develop shot-holes. 



On another occasion I infested a growing apricot bud with aphides 

 taken from a peach tree, this being the same species of aphis as that 

 mentioned above. The bud was colonised with fifteen aphides, 

 including all sizes, up to and including the winged form. 



In an hour's time they had all left the bud and settled on the stalk. 

 I did not succeed in producing shot-hole in the leaves resulting from 

 the bud thus colonised. 



These slight experiments only go to confirm the induction that 

 aphides have little or nothing to do with shot-holes. These insects 

 are very common in trees, both apricot and peach, without necessarily 

 being accompanied by shot-hole. 



On numerous occasions during these experiments I found opportunity 

 to examine with care the tissues at the edges of the " shot-holes," in 

 order to see whether or not they were infested with fungus filaments. 

 The results were so uniformly negative that I feel no hesitation, as 

 will have been already remarked, in attributing the holes in the 

 present instance almost entirely to other agencies, though I do not 

 mean by this that such holes are not frequently produced by fungi. 

 In all probability they are so produced in the majority of instances, 

 but I know for a certainty that all the appearances of the disease on 

 the apricot, as it has been hitherto known, can be produced without 

 any such fungus or microbe cause being present as would appear to 

 be in any manner adequate to the damage done. 



The method I have most frequently adopted is that of making serial 

 sections through the tissues at the edges of holes and through the 

 tissues at the location of prospective holes. These sections have been 

 cut about twenty micromillimetres thick, and have been examined in 

 various ways, with and without the intervention of stains and chemical 

 tests. 



Sections prepared in this way have been placed in cultures and 

 studied in that manner, both as to bacterial growths and fungus 

 growths, but especially the latter. 

 36567 -n 



