PRELIMINARY STUDIES ON THE YELLOW PINE. 



19 



It appears further that if not only the winter snows are lacking, but 

 the spring rains are unusually scanty, then the tree may close up shop 

 for the year and produce its final red tissue in midsummer, gaining no 

 immediate benefit from the summer rains. This appears to be the 

 interpretation of the lower diagram of figure 1. Here the same 6 big 



en 



o 



g 



c 



c 

 o 



o. 



I 



July Oct. Jan. Apr. July 



> i i i 



-Solid line=Rainfall producing; 



big doubles, 1.55 mm. 



\ 



Oct. Jan. Apr. 



Dotted line=Rainfall producing 

 big singles, 1.54 mm. 



C^ 



Dotted line=Rainfall producing 

 small singles, 0.61 mm. 



Solid line=Rainfall producing_ 

 big doubles, 1.55 mm. 



4.0 

 3.0 

 2.0 

 1.0 



4.0 

 3.0 

 2.0 

 1.0 



5.0 



4.0 

 3.0 

 2.0 

 1.0 



3.0 

 2.0 

 1.0 



FIG. 1. Effect of monthly distribution of precipitation on thickness of rings of 



growth; Prescott, Arizona. 



doubles mentioned above are plotted, together with a selected list of 

 6 small singles particularly deficient in red tissues. They are, 1904 

 double once in 10, 1902 double once in 10, 1899 single, 1895 single, 

 1894 single, and 1880 double once in 10. In these it is evident that 

 drought in the spring stops the growth of the tree. The double ring, 

 therefore, seems to be an intermediate form between the large normal 

 single ring, growing through the warm parts of the year, and the small, 

 deficient ring, ending its growth by midsummer. This occasional 

 failure to benefit by the summer rains probably explains why the 

 Prescott trees do not show an agreement of more than about 70 per 

 cent between growth and rainfall. It suggests also that the Flagstaff 

 trees, which grow under conditions of more rainfall and have very few 

 double rings, give a more accurate record than those of Prescott. 



Consistent with this view of the doubling is the condition of the outer 

 ring in the Prescott sections collected by Mr. Hinderer. These trees 



Monthly rainfall for 1909 



Monthly rainfall for 1910 



