42 



BACTERIAL DISEASES OF PLANTS 



has done a beautiful piece of work, we have perhaps something 

 akin to what occurs in the root-nodules of legumes. This is a 

 common hothouse plant, grown for its ornamental red berries 

 and thick evergreen foliage (Fig. 27). Here the bacterial injury 

 is local and internal. The bacteria are most abundant in the 

 leaf-teeth where they form pockets or cavities (Fig. 28) and multi- 





4 :>:.>rnt>>- , • 



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Fig. 29. — Section of leaf- 

 tooth of Ardisia, showing a water- 

 pore ((S') connecting with the bac- 

 terial cavity. 



Fig. 30. — A, B. Photographs of two leaves 

 of Pavetta angustifolia from Java. One show- 

 ing bacterial leaf knots; the other free. Re- 

 duced. (.Courtesy of Johanna Westerdijk.) 



ply enough to make the leaf-serratures appear blanched or yel- 

 lowish and slightly swollen, but never enough to kill them, 

 or cause the leaves to become yellow and fall. There are no 

 superficial indications of disease, except that the leaf serratures 

 gradually enlarge slightly, lose chlorophyll and become white. 

 In smaller numbers the bacteria occur in other parts of the plant, 

 including the inner parts of the seed from which they are trans- 



