5 BULLETIN 367, U. S. DEPARTMENT OF AGRICULTURE. 
tervals should show something of the changes taking place, and the 
more accurately they can be drawn the more valuable will be the in- 
formation obtainable from such a series. 
CLIMATIC CONDITIONS. 
The importance of those factors known as climatic conditions do 
not need to be argued, especially in relation to the arid grazing 
lands, where the whole crop of forage is so patently dependent upon 
them. The peculiarities of the seasons upon the Santa Rita Range 
Reserve have already been discussed by Dr. Griffiths,t who calls par- 
ticular attention to the two growing seasons and shows that they 
depend upon the amount and distribution of rainfall. 
RAINFALL 
IN INCHES 
COCCHI K 
TSE REPOS 
Fic. 4.—Curves showing the variations in the total monthly precipitation at two stations 
on the Santa Rita Range Reserve, Ariz., through a period of six years. 
The spring growing season is dependent upon the rain of the 
previous fall and winter, taken with what may fall in the spring 
proper. In April and May, and in at least a part, if not all, of 
June, there usually occurs a period of dry weather, during which 
most growth ceases and the spring annuals dry up. July, August, 
September, and sometimes part of October constitute the summer 
growing season, since it is during this period that the greater part 
of the rain falls and, the temperature being high, rapid growth 
occurs. 
Records of the rainfall by months at McCleary’s house have been 
kept since July 1, 1901. In June of 1909 a rain gauge was placed 
at MacBeath’s house and the records from both these stations are 
given in Table I. A comparison of the two records by months is 
shown in the diagram (fig. 4). 
1See Bureau of Plant Industry Bulletin 67, pp. 38—44. 
