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 
July Oct. Jan. Apr. July Oct. Jan. Apr. 
4.0}-—+--golid line=Rainfall producing —Dotted line=Rainfall producing — 
20 ___ big doubles, 1.55 mm. big singles, 1.54 mm. 
ro . Pi ee =) } 
oS 
TV ONT ORT 
Dotted line=Rainfall producing 
4.0 Ai small singles, 0.61 mm. nn 
Solid line=Rainfall producing 
2.0 
& a Xx ; ‘\ big doubles, 1.55 mm. 
eo Pa I Er) Pe i 
E \ \ 
pot 
3.0 L if \ | \ Monthly rainfall for 1909 
WEBS igcas 
10 CG a 8 OT ae 
* \ aA WA 
ei ae eS EE ee -3--9 
1.0 \ / \ / Y \ VY \\ Monthly rainfall for 1910 
AS ST BB 
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 
