202 



THE MONTHLY BULLETIN. 



make further growth because of the lack of ela])orated food supplied it 

 from the leaves. Severely diseased trees may show improper developed 

 trunks, in that they are flattened or have deep grooves directly above 

 the galls. In our study of crown gall, we have found these two charac- 

 teristics an indication of its presence. 



Fig. 71. — Crown gall, natural infection in a root of Royal Hybrid walnut two years 

 after planting from seed in a nursery where the soil was artificially inoculated with 

 minced galls. (Original.) 



GROWTHS RESEMBLING CROWN GALL. 



All abnormal growths of trees are not caused by crown gall. 



(1) Some of these other sorts of enlargements are caused by insect 

 stings or by their placing their eggs in the plant tissue. (2) Some of 

 the galls in the roots are caused by small worms called nematode worms. 

 These closely resemble small crown galls and are found on tlie roots of 

 trees and vegetables. (3) Certain species of fungi are capable of caus- 

 ing galls, one fine example of this is the galls produced on citrus twigs 

 in Cuba and Porto Rico by a fungus called Spliceropsis tumefaciens. 

 (4 ) Tubercles are found on many leguminous plants. (5) A gall 

 caused by a different species of bacteria from that of crown gall is 



