THE PARASITES OF POPILLIA JAPONICA 
49 
Sapporo,, Japan, and Suigen, Chosen, the four main centers of in- 
vestigation. These graphs show a considerable uniformity in certain 
respects, the peak in each case occurring in August and followed by a 
sharp decline. Sapporo is uniformly 6 to 10° C. (11 to 18° F. 
cooler than Yokohama, with Koiwai occupying an intermediate 
position. In Chosen, on the contrary, the summer temperatures 
approximate those at Yokohama, whereas during the winter they 
coincide closely with those of Koiwai and Sapporo. 
A comparison of these records with the graph shown in Figure 33. 
which is for Philadelphia, brings out several interesting points. The 
winter temperatures at the latter place are 4 to 6° C. (7 to 11° F.) 
above those of Koiwai, Sapporo, and Suigen, whereas the graph for 
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Fig. 32. — Curves showing the range of the mean monthly temperature for Yokohama, Koiwai, 
and Sapporo, Japan, and Suigen, Chosen. Temperature based on a three-year average, except 
Yokohama, which is for two years 
the spring months follows very closely that of the latter place. The 
maximum summer temperature is attained in July rather than August, 
and the decline which follows is more gradual. Thus it is seen that 
the growing season at Philadelphia is nearly six weeks longer than 
at Koiwai or at Sapporo, and this in a measure explains the more or 
less biennial cycle of PopiUia japonica in northern Japan as con- 
trasted with the normal one-year cycle at Yokohama and in America, 
Figure 34 shows the mean monthly precipitation for Yokohama, 
Sapporo, and Suigen, based on a two-year average, and Figure 33 
shows that for Philadelphia on a 50-year average. Unfortunately 
it was not possible to obtain records for Koiwai, and although those 
for Morioka, 10 miles away, were available yet these were in no wise 
comparable to the Koiwai figures. A heavy snowfall occurs in the 
winter months and fairly heavy rains are not infrequent throughout 
the remaining portions of the year, in fact daily showers are a rather 
notable feature. 
