Pathj4 



parasite relations - obviously the parasite is not a pathogen. On the 

 other hand, if we substitute another, less tolerant, tobacco variety, 

 brown root-rot develops, and the nematode is now acting as a pathogen. 

 You see, parasitic capability is a more or less innate, absolute, char- 

 acteristic or an organism, determined mainly by morphological character- 

 istics and physiological requirements. In contrast, the host-parasite 

 relations are quite relative, dependent upon the interaction of two 

 organisms and subject to a full range of physiological and environmental 

 factors. Parasite and pathogen are separate concepts and must always be 

 considered in that way. 



Within the framework of Koch's postulates and using the ideas and con- 

 cepts of many workers besides myself, I would like to present for consid- 

 eration a flow- sheet which I have prepared in an attempt to enable us, or 

 the basis of our research data, to define with some precision the rela- 

 tionship between the host plant and the nematode. I am then going to 

 take the liberty of illustrating some of the stages in this flow-sheet 

 with some research data of my own. 



