PLANT PATHOLOGY—JONES, 415 
our greatest hopes lie in the assurance that from now on inereasing 
attention must and will be given to the training in physiology of 
those who are coming into the profession of plant pathology. 
VII.—-THE NONPARASITIC 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 nonparasitic 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 nonparasitic diseases. If anyone doubts 
that in these nonparasitic maladies we are dealing with specific 
diseases having clearly defined symptoms which follow a regular 
course, let him grow China asters for a series of years in his garden 
and trace the course of aster yellows.1_ Here we have a malady as 
clearly characterized as a fungous rust or wilt disease; unknown, I 
believe, in Eurpoe, but widespread in America, variable with season 
and locality, yet its etiology and pathology are entirely problematical. 
But these are not problems to be undertaken lightly. Considering 
their inherent difficulties, we may be thankful that such critical and 
persistent work has been given to certain types already, notably to 
peach yellows by Smith and to the mosaic disease of tobacco by 
Mayer, Beijerinck, Woods, and others. It is encouraging to see that 
earnest attention is being given to certain apple maladies in different 
sections, especially the so-called ‘‘brown spot” or ‘‘bitter pit” in 
South Africa and Australia? 
Our encouragement will be greater, however, when we see the clear 
recognition of the fact that training in parasitology has only indirect 
value when it comes to such problems. The most evident need if we 
are to advance in the fundamentals of our research in this field of 
plant pathology is the reinforcement of our ranks with young men 
equipped with a high degree of special training in plant physiology 
grounded in organic chemistry, and ready to dedicate their services 
long and patiently to these physiological researches. 
VIII.—_THE PROBLEMS OF DISEASE CONTROL. 
Now, you are expecting the statistics showing how many millions 
America is adding to her income by modern methods in disease con- 
1 See Stone, G. E., and Smith, R. E., Mass. Agr. Exp. Sta. Bul. 79. 1902. 
2 McAlpine, D., Bitter pit investigations—First progress report. Melbourne. 
