METHOD FOE THE CONTROL OF CEOWX GALL 



Figure 6 shows the corresponding lot of trees resulting from un- 

 treated grafts which were used as checks. The variety used in each 

 case was Summer Rambo. In both illustrations the galled trees are 

 on the left, the doubtful trees in the middle, and the clean trees on 

 the right. Figure 7 shows a lot of Ben Davis trees selected as a 

 sample of some of the best results obtained from grafts treated with 

 the mercurs^ compound, and Figure 8 shows the corresponding 

 lot of Ben Davis trees resulting from untreated grafts used as checks. 

 Reading from left to right, in both illustrations, it will be seen 

 that there were no galled trees grown from the treated grafts, as 

 compared with 48 galled 

 trees in the check lot. 

 This, of course, represents 

 an example of absolute con- 

 trol that has not been met 

 with very often in the ex- 

 periments. 



DISCUSSION 



Recently R i k e r and 

 Keitt ^ have advanced the 

 working hypothesis that 

 ''the malformations dealt 

 with in the rejected nur- 

 sery trees were not induced 

 by the crown-gall organ- 

 ism.'' This hypothesis was 

 formulated because of their 

 negative results in attempts 

 to isolate the organism 

 from 175 trees which had 

 been rejected on account 

 of malformations suppos- 

 edly due to crown gall. 

 Since apparently similar 

 malformations were not 

 only controlled in size but 

 also were largely prevented 

 from forming by the actiom 

 of germicides in the writ- 

 ers* experiments, their results are not in accord with the hypothesis 

 of Riker and Keitt. It is difficult to assume that these malformations 

 are due to any agency other than a pathogenic organism, since they 

 are so definitely prevented by germicides. 



Referring to Riker and Keitt's statement that malformations occur 

 on grafts treated as aseptically as possible and " that gall-like forma- 

 tions may develop without the intervention of Bacterhnn fumefaciensr 

 attention is called to the fact that Hedgcock - performed almost iden- 

 tical experiments more than 15 years ago and arrived at the following 



Fig. 5. — One of the lots of trees which after 

 classifying, represented approximately the aver- 

 age of results obtained with the organic mercurj-- 

 compound treatmpnt. Variety. Summer Rambo. 

 Reading from left to right T Galled trees (5), 

 doubtful (11). clean (77) 



1 Riker. A. .T.. and Keitt, G. W, Crowngall in relation to nurserv stock. In Science, 

 vol. 62. p. 184-185. 192.5. 



2 Hedgcock. G. G. Field studies of the crown-gall and hairy-root of the apple tree. 

 C. S. Dept. Agr., Bur. Plant Indus. Bui. 186, 108 pp., illus. 1910. 



