456 Wisconsin Academy of Sciences , Arts, and Letters. 
This paper is not the place for details other than for purposes of 
illustration. Suffice it, therefore, to cite here a few such problems 
which are essentially physiological. (1) The relations already 
mentioned of soil temperature to the development and functioning 
of the root tubercles of legumes, a matter of keen interest alike 
to physiologist, bacteriologist, and plant culturist. (2) The rela¬ 
tion of soil temperature to the rate and character of root develop¬ 
ment. (3) The correlation between soil temperature and air 
temperature in affecting the extent and type of development of 
root and shoot organs. (4) The relation of soil and air tempera¬ 
tures to the nutritive and reproductive processes of plants, and 
consequently the proper correlation of these with the natural se¬ 
quences in the plant’s development. (5) The occurrence and pos¬ 
sible significance of bimodality in the growth curves of shoots and 
roots, there being evidence that as soil temperature is raised there 
occurs in certain cases a check in the rising curve of growth at a 
certain point (e. g., it may be about 26°-28° C.), followed by a 
subsequent rise. These are not definitely phytopathological prob¬ 
lems, nor are pathologists, as a rule, well qualified to work them 
out fundamentally. "While the phytopathologist is interested in 
the outcome in each case, he may well await patiently its develop¬ 
ment in natural course by ecological physiologists or others inter¬ 
ested in the relation of environment to the normal plant. 
There are, however, certain distinctly pathological problems for 
the development of which we cannot so wait for the help of others. 
Thus, on the one hand, we have the questions of the evident and 
immediate influence of soil temperature and other environmental 
factors on the occurrence, severity, and geographical distribution 
of certain aggressive introduced parasites. The necessity for im¬ 
mediate information along this line has been strikingly evidenced 
in recent years by the introduction into the northeastern states of 
the European parasites causing the powdery scab and black wart 
diseases of the potato. It is at once evident that our judgment as 
to how serious these are to be and what measures should be taken 
for their control must be influenced by what we know about the 
relation of our American environment to their aggressiveness. 
Other questions of the same sort come out of the recent introduc¬ 
tion of the Asiatic citrus canker into the southeastern states, the 
report last year of something resembling the Australian ‘ ‘ take-all ’ ’ 
disease of wheat in the Mississippi valley, and the possibility of 
serious Indian corn mildews coming from the East Indies. It is 
