conspectus: action on the plant 



41 



action of the parasite on the plant 



In some cases it is hard to draw the hne between parasitism 

 and symbiosis or miituahsm. Probably we shall find more 

 and more of these transition states; undoubtedly there are many. 

 I have included Ardisia in my list of genera and have excluded 

 the genera of legumes subject only to root-nodules. But a 

 nodule on the root of a legume, so far as the local condition is 



•^>, 



^'^-• 



Fig. 27. Fig. 28. 



Fig. 27. — Ardisia leaf showing swollen, white, bacterially invaded leaf-teeth- 

 J^ nat. size. 



Fig. 28. — Bacterial cavity in leaf-tooth of Ardisia crispa. 



concerned, is a disease as much as a leaf-spot, and, if Nobbe 

 and Hiltner's statements are to be credited the general effect 

 of the root-nodule organism on the plant may be excessive and 

 injurious and not to be distinguished from a disease.^ 



In the tropical East Indian Ardisia, which is one of the 

 strangest cases of mutualism known to me, and on which Miehe 



1 Smith, Erwin F. : "Bacteria in relation to plant diseases," Carnegie Inst. 

 Washington, Publ. 27, Vol. 2, 1911, p. 131, last paragraph. 



