Jones—Relation of Soil Temperature to Disease in Plants. 457 
evident in each case that information is needed in order the better 
to meet immediate economic situations, but more fundamental than 
this is the fact that the plant pathologist cannot even think, much 
less act, clearly and intelligently about any of these matters except 
as he takes into consideration the influence of environmental fac¬ 
tors. 
Another class of problems in connection with which the plant 
pathologists cannot await the help which would come too slowly 
and indirectly from outside their ranks deals with the relation of 
environment to disease resistance. We are in the habit just now 
of saying that the problems of disease resistance or of relative sus¬ 
ceptibility and immunity are the most vital problems of the day 
in phytopathology, whether we think of them in their practical 
significance or in their fundamental relations. But, in how far 
are these things clearly defined or fixed entities, in how far are 
they variables, and what may be the relation of environment to 
such possible variations? We do not wish to imply that we are 
not, in true disease resistance, dealing with definite and inheritable 
factors; the evidence is conclusive that we are. But there can be 
no doubt that environment may determine to what degree such 
factors dominate or find expression. If, therefore, we are to think 
or talk clearly and consistently about disease resistance in a plant 
we must have an adequate understanding of the influence of envi¬ 
ronment upon the development of the disease in question. 
For all these reasons we are earnest in the conviction that plant 
pathologists must continue to inquire with increasing precision 
into the relation of environment to disease development. Not 
only must they give to these problems some of their own best ef¬ 
forts, but they must seek the assistance of special workers in the 
related fields, physiologists, ecologists, geneticists, and plant cul- 
turists. Working thus in a spirit of correlation and cooperation, 
prompt and important progress is assured. 
Department of Plant Pathology, 
University of Wisconsin 
