454 Wisconsin Academy of Sciences , Arts , and Letters. 
of fully satisfactory explanations. With facts as definite and as 
clearly established as are these, however, we may hope that such 
explanation may follow in due season. 
Discussion and Conclusions 
The results here presented have been selected primarily to ex¬ 
plain what is essentially a new method of attack upon a group of 
phytopathological problems. The aim, broadly stated, is to gain a 
clearer understanding of the relation of environment to the occur¬ 
rence of disease in plants. It must be accepted as fundamental 
that environment is influential with all types of disease, and in 
each case the occurrence of a parasitic disease must evidently be 
dependent upon numerous factors. In our attempt to put the 
work upon an experimental basis, we have selected, because of 
simplicity of definition and practicability of attack, the relation of 
soil temperature to certain cases of soil parasitism. The method 
which has served well for initial studies has aimed at varying soil 
temperature while holding other factors including air temperature 
constant. Of course, it is recognized that this cannot give us all 
the data necessary to either the full explanation of such variations 
as occur in nature or the adequate interpretation of the biological 
principles involved. In either case, we must deal with the result¬ 
ants of a series of variables such as soil moisture and aeration, air 
temperature and light, transpiration and nutrition, which rarely 
operate singly or simply. Moreover, it is not to be forgotten that 
each disease as a biological phenomenon is itself always a resultant 
of the vital interrelations of two active organisms, engaged it may 
be in a struggle for existence. These relations of parasite and host 
are to be conceived of not as static or even as necessarily progres¬ 
sive in one constant direction, but rather as varying from period 
to period. Under these circumstances, one should not only ap¬ 
proach the problems with due respect for their biological complex¬ 
ity but perhaps should even present an apology for his temerity in 
grappling with them at all. The reason that seems to the writer 
adequately to justify an earnest and persistent attempt at least 
more clearly to survey the problems and to hack away at their 
most protruding angles, is that as a plant pathologist one cannot 
intelligently discuss a single disease, whether with plant cultivator 
or scientific associate, without consideration of the relation of these 
environmental factors to disease development. We cannot dodge 
