Apeil 18, 1902.] 



SCIENCE. 



611 



Two or three congenial men, having each 

 his special training in the lines indicated, 

 would be able to accomplish much more 

 in solving the difficult problems which con- 

 front us than any single man. But I can- 

 not divorce myself from the thought that 

 the pathologist should himself be a chemist 

 and a physiologist. There must certainly 

 be a deeper study of the intimate nature 

 of the plant in health and disease if we 

 are to determine just what constitutes im- 

 munity in many given cases and just what 

 is the best method of checking the preva- 

 lence of many of our most vexatious dis- 

 eases. I may refer, for example, to the 

 difficulties which lie in the way of under- 

 standing the action of even so well studied 

 and simple a thing as Bordeaux mixture. 

 In recent years we have hes,rd a good deal 

 about injuries due to the Bordeaux mix- 

 ture, especially on the peach and plum. 

 WHiy are these trees more susceptible than 

 the apple and the pear or the grape? Why 

 does Bordeaux mixture appear to be more 

 injurious one season than another season, 

 or in the hands of one man than in the 

 hands of another man? Only an intimate 

 knowledge of the nature of this substance 

 and of the chemical physiology of the 

 plants themselves can furnish an answer 

 to these questions.* I may refer also to a 

 whole group of diseases, the etiology of 

 which mere field study and the ordinary 

 laboratory methods do not appear to be 

 competent to unravel; for example, the 

 California (Anaheim) vine disease, the 

 wilt of the orange, the sereh disease of the 

 sugar cane, gum diseases, the yellows and 

 rosette of the peach, the winter blight of 

 the tomato, the internal brown spotting 

 of potato tubers, etc. We may confidently 

 expect that these obscure diseases will 

 yield up their full etiology to careful study 



* Since this was written considerable light has 

 been thrown on the snbject by Mr. J. F. Clark 

 {Bot. Gaz., January, 1902, p. 26). 



at some time in the future, but it will have 

 to be a more thorough and exhaustive study 

 than any that has yet been given to it and 

 by men better trained for the solution of 

 the special problems involved. A good 

 beginning on this class of diseases has been 

 made by Beyerinck and Woods in the study 

 of the Mosaic disease of tobacco. 



In the time which has passed, much at- 

 tention has been given to the parasite and 

 comparatively little to the host plant. The 

 plant has seemed to many in the nature of 

 a passive agent. This is far from being 

 the true state of the case. In time to come 

 I would not have the parasite studied less 

 (it must be inquired of with still greater 

 care, especially as to what are its limits in 

 the use of foods, and in the toleration of 

 non-foods), but I think that the host must 

 also, certainly, be studied more diligently 

 if the wonderful progress in plant pathol- 

 ogy during the last two decades is to con- 

 tinue. To my mind, the problem of prob- 

 lems in pathology, both animal and vege- 

 table, during the next fifty years will be the 

 varying nature of the host plant or host 

 animal as related to the parasite. This 

 is the burning question. Why is it that 

 some individuals are so very susceptible to 

 disease and others so resistant? Why is 

 it that the same organism is more suscep- 

 tible at one age, or at one time or season, 

 than at another? These are questions in- 

 timately connected with structure and with 

 changes in secretion and excretion, i. e., 

 with the complex chemistry and physics 

 of the individual body, and we shall never 

 be able to solve the difficult problems of 

 plant immunity and put our knowledge 

 into practice for the prevention of diseases 

 until we have a much more intimate ac- 

 qaintance with the plant cell as a chemical 

 laboratory, or as a physio-chemical labo- 

 ratory, if you prefer that term. When we 

 are able to point out clearly just what the 

 chemical and physical changes have been 



