EXPERIMENTAL WORK ON THE RELATION OF SOIL 
TEMPERATURE TO DISEASE IN PLANTS 
L. R. Jones 
Any branch of science in the making must proceed from the 
more obvious to the more fundamental, from observation to ex¬ 
periment. Plant pathology as the youngest offshoot of botanical 
science is in the early stage of its evolution. One of its most ob¬ 
vious aspects is the relation of weather to the occurrence of plant 
disease. Every wheat farmer knows from experience that whether 
or not his grain rusts depends upon rain and sun, and the po¬ 
tato grower fears that a wet autumn may rot his tubers. These 
evident relations of weather to rust and mildew were discussed 
in the Roman classics, but naturally effect and cause have been 
much confused even in the mind of the scientist until within a 
century. With the establishment of the germ theory of disease 
in animal pathology came, simultaneously, the proof of the causal 
relation of parasitic organisms, fungi, and later bacteria, to plant 
diseases. Since about 1850 botanists have generally accepted the 
evidence that the smuts, rusts, mildews, and similar fungi are 
genuine parasites and have held them to be true causes of plant 
diseases. But the keenly observant though less scientific farmer 
continues to blame the weather when his wheat rusts, his grapes 
mildew, or his potatoes blight. 
The final analysis requires, of course, consideration of both 
factors, the parasite as the active cause, the weather as a possible 
controlling factor in its operation. The challenge to the phyto¬ 
pathologist who aims at working his problem to the finish is to de¬ 
termine by critical experiment the relation of environment to 
parasitism. While the fundamental importance of this has long 
been recognized by pathologists, and while we have innumerable 
observational data, comparatively slow progress has been made 
with exact experimentation. This has been due, not to lack of 
28—S. A. L. 433 
