Jones—Relation of Soil Temperature to Disease in Plants. 455 
the issues as plant pathologists; we ought not to wish so to do as 
biologists. The knottier the problems the clearer the challenge. 
We have purposely selected samples where the evidence is relatively 
Simple and direct and have aimed to show that it is convincing at 
least upon certain points. We have not done this with the inten¬ 
tion of misleading as to the inadequateness of the progress already 
made. Each step has made clearer the complexities of the maze 
we are treading. The purpose has been, however, to show, first, 
the worth-whileness of tackling the problems, and, secondly, that 
worth-while progress is possible by the methods outlined if the at¬ 
tack is earnest and persistent. 
On the other hand, any plant pathologist should wisely hesitate 
to undertake work upon such a complex of problems with any 
hope of going far working singlehandedly or alone from the path¬ 
ologist’s viewpoint. As was explained at the outset, much of the 
progress made in the work here summarized has been due to the 
happy correlation of the efforts of a number of graduate students 
as supplementing and greatly extending what any of the depart¬ 
mental staff members alone could have accomplished. But num¬ 
bers alone will not get us far if all work at the same angle. Im¬ 
mediately as the problems take form, it is evident that at bottom 
we are dealing with basic questions of the physiology of the host 
plant on the one hand and of that of the parasitic fungus on the 
other. Here, again, our courage as plant pathologists has been 
kept up because of our confidence in our physiologically minded 
associates as advisers or co-workers. 
We must not, however, assume that by so defining these prob¬ 
lems as basically physiological we thereby transfer to the already 
overburdened plant physiologists the responsibility for the imme¬ 
diate prosecution of their investigation. If any men specially 
trained in plant physiology can be induced to take up work in this 
field, it will be immediately to the advantage of pathology. On the 
other hand, it cannot be expected that much help will come 
through distracting mature physiological investigators from their 
own chosen lines of interest. It is, however, evident that this 
work thus far has already defined problems which are distinctly 
physiological rather than pathological and which have such broadly 
attractive scientific interest that we may safely await their further 
development by plant physiologists aided in some cases by workers 
in other lines of applied botany. 
