io6 
L. R. JONES 
analyzing such data, while all local pathologists pledge the undertaking 
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 para- 
site 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 scientific 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 our 
greatest hopes lie in the assurance that from now on increasing atten- 
tion must and will be given to the training in physiology of those who 
are coming into the profession of plant pathology. 
VII. The Non-Parasitic Disease 
If the early workers in plant pathology erred in failing to recognize 
the importance of parasites as causal agents, the recent ones have 
gone to the other extreme. 
The mycologist and the bacteriologist naturally bring to our 
attention even the minor parasitic maladies, the physiologist has as 
yet rarely come to our aid. It is only as one undertakes the compre- 
hensive study of the maladies of a particular host that he realizes how 
few of the non-parasitic diseases have been listed. 
Perhaps the peach, the tobacco and the potato are the only plants 
where the energies have been duly distributed between the investi- 
gations of parasitic and non-parasitic diseases. If anyone doubts 
that in these non-parasitic maladies we are dealing with specific 
