THE MONTHLY BULLETIN. 



605 



shown in Figure 342 was inoculated on February 27, 1912, with a bit of 

 bark from a tree just about to die. It was first noticed to be gumming 

 on May 24th. Figure 342 was photographed August 2d, and Figure 

 343 September 19, 1912. The leaves on the side of the tree which was 

 gumming showed a decided yellowing, while the other side was still 

 green. By March 11, 1913, there was left only four inches of live bark 

 on the opposite side. Cuts into other trees inoculated with healthy bark 

 healed perfectly without gumming. Many other trees inoculated at the 



♦^ 



. .^-W, 



Fig. 343. — Same tree as in Fig. 342 photographed 

 September 19 th to show the rapid progress of the 

 disease. (Original.) 



same time and also at later dates with diseased tissues were similarly 

 affected. 



The Causal Agents : Having found that the disease was transmissible, 

 the next step was to find out what the agent or agents were that were 

 capable of transmitting it. In making the first studies of lemon gum- 

 mosis in the orchards it had been noticed that there were at least two 

 forms of the disease: one in which the outer layer of bark was killed 

 much in advance of the inner and in "which there was some softening qf 



