324 PLANT DISEASES 



TOMATO BLACK ROT 



(^Macrosporiiim tomato, Cooke.) 



This disease appears to be present wherever the tomato 

 is cultivated. The fruit is most frequently attacked, but 

 the fungus is also often present on the stem and leaves. 

 The fungus is a wound-parasite, and on the fruit most 

 frequently effects an entrance through minute cracks round 





Fig. 89. — Macrosporium tomato. 1, a diseased tomato ; 

 2, conidia of the fungus in various stages of develop- 

 ment, X 300. 



the Style, or at the point of insertion of the stem, but may 

 appear on any part of the fruit where a puncture of the 

 skin large enough to admit of the entrance of the germ-tube 

 of a spore is present. A dark-coloured mycelium forms 

 in the tissues, and rapidly destroys the cells, consequently 

 the area occupied by the fungus sinks a little below the 

 general surface of the healthy part of the fruit. At a later 

 stage the sunken surface of a diseased spot becomes covered 

 with a delicate, velvety pile of a brownish or blackish-olive 

 colour. Microscopic examination shows this pile to consist 



