SPRING PRECIPITATION AND HEIGHT GROWTH 



679 



pected, there is no apparent relation between height growth and annual 

 precipitation, summer precipitation or winter precipitation ; in fact, the 

 growth from year to year often varies inversely with the precipitation 

 for any of these periods. When it is considered that of the total an- 

 nual precipitation at Fort Valley, the mean amounting to 'about 23 

 inches, approximately 40 per cent comes during the winter months 

 (December-March), 30 per cent during July and August, and less than 

 10 per cent during the spring months (April and May), the foregoing 

 statements are startling. 



Figure i. — Seasonal precipitation and annual height growth of western yellow pine 



saplings from 1909 to 1917. a. Annual precipitation; h. Winter precipitation (December- 

 March preceding the corresponding year's growth); c,^ Summer (July-August) precipitation; 

 d. Annual height growth; e. Spring (.\pril-May) precipitation. 



In order to clarify the problem, it is necessary to analyze the growth 

 habits of western yellow pine as well as the climatic and soil conditions 

 under which it grows in this locality. The terminal shoots begin to 

 elongate about the middle of May, and by July i they have practically 

 completed their growth. Thus it appears that the entire height growth 

 occurs during the period of lowest precipitation of the year. From 

 the middle of May to the middle of July the rainfall is normally less 

 than one-half inch, and comes in such small showers as to be of no 

 benefit to deep-rooted plants. It is evident, therefore, that the moisture 

 utilized in making this growth is drawn almost entirely from a stored 



