1915] 



SMITH — -BACTERIAL DISEASES OF PLANTS 



393 



ACTION OF THE PARASITE ON THE PLANT 



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

 and symbiosis or mutualism. Probably we shall find more 

 and more of these transition states. 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 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 or- 

 ganism on the plant may be excessive and injurious and not 

 to be distinguished from a disease. 1 



In the tropical East Indian Ardisia, which 



of the 



strangest cases 



of mutualism known to me, and on which 

 Miehe has done such a beautiful piece of work, we perhap 



have 



mething akin to what 



the root nodules of 



legumes 



He 



the bacterial injury is local and internal 



There are no superficial indications of dise 



The bacte 



most abundant in the leaf-teeth where they form pockets 

 savities and multiply enough to make the leaf serratures 

 ear blanched or yellowish and slightly swollen, but never 



gh to kill them 



In smaller numbers the bacteria 



in other parts of the plant including the inner parts of the 

 seed from which they are transmitted to the seedling, whose 

 leaf serratures, infected through their water-pores, in 



become the chief focus of the bacterial multiplication 



Ap 



parently the bacteria are always present, and we do not 



what would happ 



Ardisia plants 



without 



them, nor do we know how to obtain such plants. It would 

 be an interesting experiment to see if they could be produced 

 and to watch their behavior. 



The action of such organisms as I have mentioned differs 

 probably from the behavior of active parasites in that they 

 liberate much weaker toxins and enzymes, can attack only very 

 actively growing parts, and also give off compensating nitrog- 

 enous substances. Not yet proved for Ardisia. 



1 Smith, E. F. Bacteria in relation to plant diseases. Carnegie Inst. Wash- 

 ington, Publ. 27 2 : p. 131, last paragraph. 1911. 



