324 11. The Training Problem 



As the questions of ininiimity bulk so largely at the present day some 

 knowledge of the chief results in this relation of medical bacteriology 

 is valuable, though I for one do not hold the view that the knowledge 

 of toxins or anti-toxins, of lysins, precipitins, and agglutinins, knowledge 

 which has been derived from the specialised study of medical bacterio- 

 logists, is likely to give us new weapons in the attack on economic 

 problems of plant pathology. 



The days when the only weapons for dealing with plant disease were 

 the tracing of the life-history and the destruction of the parasite at some 

 point in its life-cycle or the prevention of infection by sprays, are now 

 fortunately j:)ast, since in many cases the fungus cannot at present be 

 destroyed and the use of sprays is very often impossible. The importance 

 of immune and resistant varieties has come to the front and it has been 

 found that such varieties can be bred or selected. The student of mycology 

 who is to undertake investigation of practical importance must therefore 

 have a knowledge of the results which have been obtained in this direc- 

 tion. One man, however, cannot combine the capacities of a plant 

 pathologist and a plant breeder as has, I know, been expected in some of 

 our tropical dependencies. The two workers must unite their forces and 

 make a combined attack. 



I come now to the question of the physiological aspects. Disease is 

 abnormal physiology, so the physiological outlook is a very necessary 

 one, and I am glad to see that the importance of this aspect has been 

 stressed by both Dr Russell and Mr Chittenden. It has long been recog- 

 nised that the environmental conditions have a marked influence on 

 infection; this they do by affecting the physiological reactions of both 

 host and parasite. The physiological conditions for infection and the 

 physiological processes connected with it are a field of work in which our 

 knowledge is still only just beginning. The fact that different kinds of 

 manuring may markedly afiect the degree of infection, and that changes 

 of climatic conditions may even affect the development of a fungus 

 already within the host, show clearly the importance of the physiological 

 aspects of plant pathology. Another question of fundamental importance 

 in plant pathology is that of the physiological differences between immune 

 and susceptible hosts. Also the growing importance of what may be 

 called plant hygiene in reducing the incidence of disease shows the 

 importance in plant pathology of the physiological conditions of the 

 host plant. It is clear from this that the student requires a knowledge 

 of the outlook of modern plant physiology, and therefore some training 

 in modern plant physiology is necessary, and this of course necessitates 



