E. M. Doidgk 13 



sterile knife and dropped into a tube of sterile distilled water; from 

 this a series of plates was poured. 



A different method was adopted with the leaves because the organism 

 diffuses very slowly into water from the leaf tissues. A leaf was washed 

 in 1 : 1000 mercuric chloride, then in several lots of distilled water. 

 A glass pestle and mortar similarly treated, and then an infected part 

 of the leaf ground up in it with some sterile sand and a little distilled 

 water. A drop of the liquid was put into a tube of medium and plates 

 poured. 



After the organism had been repeatedly isolated in the way described 

 above, attempts were made to infect a number of young mango trees. 

 The inoculation work has been rendered difficult by the entire absence 

 of any greenhouse accommodation. The trees do not thrive in the open 

 in Pretoria and though they have flowered for two seasons they have 

 not developed any fruit. 



It has already been shown that the majority of the natural infections 

 take place in vigorously growing tissues during a spell of wet weather. 

 There have been three very dry seasons since the inoculation work was 

 commenced (1911 — 12), and it is almost impossible to obtain infections 

 in the open in dry weather. 



The few successful inoculations described below, were obtained 

 during a short spell of rain and cloud. There have been a proportionally 

 large number of failures, but in no case have any of the control plants 

 become infected. 



This phase of the work will be continued as soon as suitable green- 

 house accommodation is available. 



Direct infection experiments. 



1. A small portion of the gummy substance exuding from an 

 infected spot on a mango fruit was inoculated by needle pricks into the 

 stem and petioles of a young mango tree. After about four weeks there 

 were discoloured areas round the needle pricks, later longitudinal 

 cracks were formed. The following season these stem and petiole 

 infections were responsible for a number of spots in the leaves in their 

 immediate vicinity. The controls remained healthy. 



Cultures of the organism were obtained from the discoloured areas, 

 whose tissues were crammed with bacteria. 



2. Portions of diseased tissue were crushed, and the bacteria 

 allowed to diffuse in sterile distilled water. Part of the liquid con- 

 taining the bacteria was then allowed to stream over both surfaces of 



