412 



A Tomato Canker 



In the fruit a similar disorganisation of cells takes place, but the 

 hypodermal cells at the edge of the injured tissue begin to divide actively 

 (Fig. 2) and sometimes form a complete layer of new cells under the 

 disorganised tissue (Fig. 3) ; this accounts for the convex contour of 

 the canker. Sorauer(5) has illustrated a similar condition as a result of 

 hail injury; it is probable therefore that the multiplication of cells is 

 not due directly to the action of the organism but to the presence of 

 dead tissue in the rapidly growing fruit. 



Fig. 3. Section through lesion on fruit, showing complete layer of actively dividing cells. 



The nuclei in the affected cells become much hypertrophied, be- 

 coming five or six times the size of nuclei in healtby cells. The nucleolus 

 becomes very large and vacuolate, and the nucleolar membrane dis- 

 appears. There are frequently two nuclei in a cell or two nucleoli in one 

 nucleus, the latter frequently irregular or lobed, being similar in shape 

 to nuclei dividing amitotically as found by Smith (4) in crown gall lesions; 

 but there was no clear evidence that the nuclei were dividing in this way. 



