CAUSE AND NATURE OF CROWN-GALL 11 



ing failed to find either an animal or vegetable parasite which 

 would account for it, and not attempting to ascertain the readi- 

 ness with which it can be communicated from one tree to 

 another, have tried to account for the outgrowths in other 

 ways rather than by infection. Nearly all investigators, how- 

 ever, have observed that its appearance in certain orchards and 

 in certain portions of orchards, and more particularly in defi- 

 nite restricted areas in nurseries, is suggestive of parasitic 

 origin. Selby, Woodworth, and Halsted have each had the 

 disease under observation for several years, and have called 

 attention to the probability of its communicability, but have, 

 for the most part, refrained from making positive statements 

 regarding it. Halsted,'- by planting peach pits in soil with 

 minced galls from the peach, found that the seedlings when 

 seven months old were much more badly infested than similar 

 seedlings grown in the same kind of soil without the minced 

 galls. His experiments, however, were defective, in that he 

 obtained some diseased trees among the check plants. I cpiote, 

 however, the following as his conclusions : 



' ' The results point to the conclusion that the peach crown- 

 gall is decidedly contagious, and with the seedlings surrounded 

 with minced peach galls the affection is almost certain to appear 

 and in a violent form." 



Selby 11 ' in his experiments transplanted a number of healthy 

 peach trees to within about eight inches of a diseased peach 

 tree of same age, and found that 25 per cent, of the healthy 

 trees became affected during the first two seasons, while a 

 number of healthy trees transplanted at the same time in simi- 

 lar soil, but not in the vicinity of diseased trees, remained at 

 the end of the two seasons in perfect condition. His conclu- 

 sions are as follows : 



" In so far as present light enables one to judge, the conclu- 

 sion that the crown-gall is a contagious disease appears to be 

 warranted." 



Woodworth frequently calls attention to the apparent conta- 



18 Rept. Bot. N. J. Agr'l Rxp. Sta. 1895, 413. 

 19 Bull. Ohio Agr'l Exp. Sta., 92, 213. 



