EXPERIMENTS WITH THE PEACH ORGANISM. 67 



Inoculations of January 13, 1908 (Smith). 



One hundred and thirteen seedhiig peach trees 1 year old were 

 received through Mr. Corbett from the ArHngton Experimental 

 Farm. All of them were in good condition except 5, which were 

 rejected because of borers. All were free from nematode galls and 

 also from crown galls. Twelve were given to Doctor Townsend. (See 

 Rose on Peach, p. 76.) The remaining 96 were divided into 2 lots. 

 The dirt was first thoroughly washed from the roots; then the roots 

 were shortened a little and the tops pruned back, so that they could 

 be planted in 10-inch pots in the hothouse. The 2 groups were then 

 treated as follows: 



(1) Thirty-six trees were held as absolute checks, 15 pricks in 

 groups of 5 being made with a sterile needle on the roots of each tree. 

 The check pricks on all the plants were made before any inoculations 

 were undertaken. 



(2) This group of 60 trees is like group 1, except that opposite 

 the 15 check needle pricks (3 groups of 5 each) 15 infected pricks 

 (introducing a pure culture of the organism from crown gall of the 

 peach) were made on the crown and roots in groups of 5 each. The 

 side on which the check pricks were made was marked by cutting 

 a shver out of the bark of the stem, above the crown, with a sharp 

 knife. A good deal of the white slime was put on the roots in making 

 these inoculations (in most cases on the main root, rarely on side 

 roots), and as they were planted within an hour or two of inoculation, 

 there was a possibility of the slime infecting some of the check 

 pricks by finding its way to the other side of the root; with a view 

 to lessen this possibility, instructions were given the gardener to with- 

 hold water until the following day, if this could be done without injury 

 to the trees. They were planted in good greenhouse soil. 



Result. — March 4, 1908: The peach trees planted January 13 were 

 pulled up and examined: 



(1) Group of 36 check plants: 33 absolutely sound, 3 with slightly 

 enlarged callus about as many knife wounds, none with galls. The 

 trees received 540 stabs, all of which healed normally. 



(2) Group of 60 inoculated plants: 55 with galls; 5 free. The 55 

 plants bore 127 galls — with very few exceptions, only where inocu- 

 lated. The few exceptions are minute galls in the vicinity of the 

 pricks on smaller accidentally injured roots. The 900 check pricks 

 remained free from galls. The best galls were photographed (PI. XI, 

 fig. 3) and put into alcohol. None were very large, but sufficient 

 for the time concerned, i. e., less than 2 months — the largest one- 

 half to five-eighths inch in diameter. 



Had the trees been ready to leaf out when planted it is probable 

 that the percentage of infections would have been 100 instead of 92. 



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