PLANT BACTERIA, VOL. 2. 



PLATE 3. 





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Black Spot of the Plum, 

 (i) Surface of a green plum (x 10), showing a white speck 'stomal in center of a very small spot, due to Bad. pruni. 



This is the earliest stage of the disease clearly visible to naked eye. Each of the numerous white specks has 



a single stoma in its center. 

 (2) One of the tiny white specks more highly magnified so as to show the central stoma, x 200 (?). 

 (3 and 4) Two sections through a normal stoma on the green fruit, showing empty sub-stomatic chamber; one 



passes through the center, x 200 ('). 

 (5) A group of small spots on a green Hale plum, each of the smaller ones showing clearly a stoma in its center 



xioC?). 

 (6 and 7) Small spots (x 10) showing bacterial exudate. Spots further advanced than in fig. 1. In fig. 6, bacteria 



were issuing from 30 or 40 stomata, but, as in fig. 7. the central drop is larger. The reason for this is apparent 



at once on cross-section (see plate 5). 



