414 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
times stimulating. But we have scarcely sufficient basis for a sugges- — 
tion as to the nature of the agents involved. Such problems call for 
the combined skill of pathologist, physiologist, cytologist, and 
chemist. 
The variation in the occurrence of disease with environment is one 
of the commonest observations and a thing of the greatest practical 
moment. Yet how little progress we have made in understanding 
the factors. Climate and soil both are composites of many variables, 
which in turn may react on either host or parasite. Why is it that 
Rhizoctonia diseases and Blattrollkrankheit of the potato claim so 
much attention in certain sections of the United States while in 
others pathologists are skeptical as to their existence? Why is it that 
the bacterial black leg of the potato develops so much worse in the 
South than in the North? Why is it that with the melon the Fusarium 
wilt is the scourge of the one section and the bacterial wilt of another ? 
Why is it that the yellows disease of cabbage exterminates the crop 
under certain conditions and is of minor importance under others ? 
It would seem that here are problems to challenge the attention 
of every pathologist. Yet if one turns to them he is balked at the 
outset. We have inadequate data as yet regarding the occurrence 
and distribution of even the commonest economic diseases in the 
United States. Let us unite in urging that in the reorganization of 
the work now in progress in the Bureau of Plant Industry the entire 
attention of at least one expert pathologist be given to collecting and 
analyzing such data, while all local pathologists pledge the under- 
taking continued support and cooperation. Coordinate with this, 
the local student of the special disease may make painstaking studies 
in field, greenhouse, and culture chamber, and in time delimit the 
effects of moisture, temperature, soil reaction, and like factors upon 
each parasite and host. 
The evidence is accumulating that the variations in relations 
between parasite and host which give us specialized races of parasites 
on one hand, and on the other, gradations in disease resistance of 
host are of the greatest importance, whether scientifie or practical. 
But we can as yet record little that helps us adequately to define the 
factors in the problems, much less to solve them. 
As suggested before, these problems are at bottom physiological 
and of the most complex kind. The pathology of the past has been 
the work of the mycologist and the bacteriologist. That of the 
future must be increasingly dependent upon the physiologist; for what 
is pathology at bottom but abnormal physiology? Realizing how 
slow is progress upon the really fundamental problems in normal 
physiology and what dearth there is of workers adequately trained to 
grapple with them, we must be patient with ourselves, and beg the 
patience of others, when dealing thus with the abnormal. Perhaps 
