474 
Journal of Agricultural Research voi. xxi,No. 7 
freedom from disease must be considered as related primarily to its 
entire growing season. They provide no specific indications as to the 
relation of temperature to the various periods of the growth and develop¬ 
ment of the potato plant. So far as is known to the writer, no one has 
given close attention to the effect of soil temperature on growth of the 
potato during the first four or five weeks of its development, at which 
time the “ Rhizoctonia” disease is most destructive. 
POO 
/so 
m 
m 
zoo 
80 
00 
40 
V 
o 
S /e /& /8 ?/ 
Fig. 5.—Relation of soil temperature to the severity and to the distribution of the injury caused on potato 
stems by Corticium vagum (experiment 5). 
In the course of the greenhouse experiments, observations were made 
as to the reaction of the normal potato plant at the various soil tempera¬ 
tures. The data are seriously limited by the fact that such observa¬ 
tions were of necessity confined largely to an early period of growth of 
a comparatively small number of control plants. The results, however, 
appear of sufficient interest to warrant their inclusion. 
The data from the various experiments emphasized somewhat clearly 
the importance of the rate of growth of the young shoot during the period 
