Ethel M. Doidgk 413 



In the entirely disorganised cells the nucleus continues to increase in 

 size until the nuclear membrane is ruptured and the chromatin becomes 

 diffused; the nucleolus remains intact for a considerable time, taking 

 a red stain and standing out clearly in the disorganised mass. 



Isolation of the Causal Organism. 



The organism was first isolated in January, 1914, from tomatoes 

 purchased on the Pretoria market. On these plates a yellow organism 

 was predominant, but there were also colonies of a spreading, cream- 

 coloured organism. At that time no greenhouse accommodation was 

 available, and attempts to inoculate tomato plants out of doors during 

 a spell of dry weather were unsuccessful ; it was quite impossible to keep 

 the atmosphere sufficiently moist. Attempts to inoculate detached fruits 

 in the laboratory also proved a failure. 



The disease was noticed on fruit exposed for sale each summer, but 

 there was no further opportunity to investigate the matter until 

 February, 1920. The organism was again plated out from fruit exposed 

 for sale on the Pretoria market; colonies were visible after 48 hours, 

 at 30° C, and in three days assumed their characteristic form and yellow 

 colour. An almost pure culture was obtained direct from the host. The 

 colonies were very similar in appearance to those of Bacterium citri, 

 B. campestre and other related organisms; there appears to be a large 

 number of plant parasites belonging to this group. 



During March, 1920, the organism was repeatedly isolated from 

 scabby fruit and infected leaves collected in a market garden at Daspoort, 

 near Pretoria. In each case a pure culture of the organism was obtained 

 without difficulty, from both leaf and fruit. It is more easily isolated 

 from the fruit since the surface can be sterilised and the culture made 

 from the tissue underneath. 



Inoculation Experiments. 

 Preliminary Experiments. • 

 A. 



28. 1. 20. Two well-grown tomato plants were used bearing green fruit, almost 

 full grown. The fruits were inoculated with a culture isolated from tomato fruits 

 purchased on the Pretoria market. The culture was applied with a camel's hair 

 brush, a few tomatoes on each plant being pricked and the rest uninjured. Inoculated 

 fruit was covered for 24 hours with beakers covered with brown paper and plugged 

 with cotton wool. 



