IIKIGHT GROWTH AND WEATHER COXDiriONS . 865 



the latter part of April or lirst of May and is practically complete for 

 the season by the middle or end of Jvily. Climatic records for the 

 months of April, May, June, and July are, therefore, all that need be 

 included in a study of the direct relation between climatic variations 

 and rate of height growth. A summary of the climatic data for these 

 months in the years 1912, 1913, 1914, 1915, and 1916, for meteorological 

 station number 3 at the Priest River Experiment Station, is given 

 in Tables 4, 5, and 6. 



The observations which form the basis of the climatic records were 

 made by Forest Service officials in co-operation with the U. v'^. Weather 

 Bureau. Standard meteorological instruments were used. 



In temperature, the year 1914 shows somewhat higher figures than 

 the other years, ranking first in the months of May and July and rank- 

 ing slightly the highest for the four-months' period as a whole. A lead 

 of 2.1 degrees above the average for the month of May, in the year 

 1914, would indicate more than ordinarily good growing conditions, 

 particularly if accompanied by plenty of moisture. There is, however, 

 a considerable and rather inconsistent variation in temperature for the 

 five years as a whole, and it seems doubtful if much weight can be 

 given the indications of mean monthly temperature taken separately. 



A definite lead is shown by the year 1914 in the number of ''clear" 

 days, both in the average and for the months of May, June, and July — 

 the growing months. This, when coupled with the higher than average 

 temperature conditions in that year, would be favorable to an unusual 

 amount of growth, other factors being equal. 



Precipitation figures, in the form of monthly totals, are contradictory 

 and show no distinct tendencies. The response which the growing 

 plant makes to differences in amount of precipitation is apt to be very 

 indirect unless the amounts apprcjach the minimum needed by the plant. 

 Excessive anKnnits beyond what the plant requires and can utilize under 

 the given temi)erature and light conditions will produce little, if any, 

 effect in the form of growth. It is evident from the figures in Table 6 

 that in some months an exceptionally heavy precipitation occurn-d. 

 which was probably more than the trees conld utilize fully. Moreover, 

 this was often largely concentrated during short periods, making a con- 

 siderable portion of the total iniavailable for the use of the tree because 

 of heavy loss in run-ofi". 



In order to determine whether an analysis of tiie daily precipitation 

 would bring out any relationshijis between rainfall and grow tli the dail\- 

 amounts were i)latted. as show 11 in fignrc i. 



