THE MONTHLY BULLETIN. 



603 



Lines of Investigation. 



Was gummosis infectious ? Inoculations were first made to determine 

 either the infectious or non-infectious nature of certain forms of gum- 

 mosis. Cuts M^ere made into the bark of large, healthy lemon trees and 

 bits of material from diseased trees inserted. It was found that typical 

 cases of gummosis (the dying of large areas of bark and the exuding of 

 gum) could be induced on perfectly healthy lemon trees in three to four 

 months by bits of discolored bark or wood taken from the advancing 

 edges of diseased areas of naturally occurring cases of gummosis. Bits 

 of exuded gum or pieces of tissue already permeated with gum from 

 these same trees failed to transmit the disease when placed in cuts in 

 the bark of healthy trees. This result appeared to explain why mocu- 



Fig. 340. — Lemon tree inoculated by 

 inserting under the healthy bark a 

 bit of gummosis barlt from a diseased 

 tree March 8, 1912; photographed 

 June 27, 1912, to sliow exuding gum. 

 (Original.) 



Fig. 341. — Opposite side of same tree 

 shown in Fig. 340: bark cut without in- 

 tion of diseased tissue. (Original.) 



lation by previous workers had failed. The infectious principle was 

 not in the gum itself, but in the diseased bark and at the margins of the 

 enlarged areas, and therefore inoculation with the gum alone had failed 

 to transmit the disease. It was also found that the younger the trees 

 the more resistant they seemed to be to the effect of inoculations. Young 

 nursery stock could readily be induced to gum, but usually healed up 

 again without further progress of the disease. In older trees, however, 

 the gumming continued and the area of killed bark slowly increased. 



