16 Bacterial Disease of the Mango 



Morbid anatomy. 



Some difficulty was experienced in obtaining good sections, as the 

 tissues, especially of the leaves, are very tough and are apt to tear out 

 of the paraffin. The best results were obtained after fixing in acetic 

 alcohol, which was used hot ; and embedding in paraffin in M.P. 60°C. 

 The stain which gave the best result was a combination of Ziehl's carbol 

 fuchsin with light green. 



The organism causes no hyperplasias and appears to be entirely 

 confined to the parenchyma. It makes its way into the tissues through 

 a slight abrasion of the surface ; it seems very probable that it can also 

 gain an entrance through the stomata, but I have not yet been able to 

 obtain sections which would establish the fact. When once it has 

 effected an entrance, the organism multiplies rapidly and invades the 

 surrounding tissues (Plate VII). The bacteria are very plentiful in the 

 intercellular spaces, and appear to wedge apart the cells and dissolve 

 the middle lamella (Plate IX) ; one frequently notices in sections 

 through the fruit, a cell which is apparently still untouched, but is 

 completely isolated and surrounded by masses of bacteria. 



In some cases the bacteria appear to be intracellular also, but it is 

 almost impossible to judge whether this is really the case or whether the 

 rods have been dragged over the surface of the cells in sectioning; 

 probably the latter. 



A good deal of gummosis takes place during the destruction of these 

 cells, the walls of which become swollen and discoloured. The dis- 

 colouration does not appear to be due to any staining caused by the 

 bacteria but to the decomposition of the cells which are attacked. 



The swelling of the disorganised cells'is so marked that even in the 

 leaf the surface of the affected area appears raised to the naked eye. 

 The increased thickness of the diseased region is well shown in the 

 section photographed in Plate X. In the fruit this is even more 

 marked and so also is the exudation of gum from the diseased tissues. 



The nuclei of the cells in the affected area are abnormally large, and 

 stain deeply with the fuchsin ; they are very conspicuous in sections 

 through young infections on the fruit. 



As the tissues become disintegrated and the cells killed, the bacteria 

 disappear from the dead areas and are found in more deep-seated 

 tissues (Plate VIII). They do not appear to be capable of attacking 

 lignified tissues in a number of sections examined there was no trace 

 of bacteria in the nbro-vascular bundles of fruit or leaf, although the 



