290 SOILS. 



the calendar year, as the unit or reference for crop production. 

 There the crops depend upon what rainfall may occur from 

 October to May, there being no summer rains of agricultural 

 significance, and outside of irrigated lands, almost all vegeta- 

 tion save that of trees being in abeyance. In India, there are 

 two distinct growing seasons (" kharif " and " rabi "), corre- 

 sponding to the two " monsoon " seasons; and no matter how 

 much rain may fall during one, almost total failure may occur 

 in other tropical and arid sections of that country. 



The Daily Variations are of interest chiefly with respect to 

 health conditions, since most plants are more adaptable in this 

 respect than the average man. 



RAINFALL. 



Distribution Most Important. The summary statements of 

 the annual rainfall are almost equally as deceptive as are those 

 of annual mean temperature, since quite as much depends on 

 the manner in which it is distributed through the year, as upon 

 its absolute amount ; and also upon the manner of its fall. 

 Thus Central Montana has the same aggregate annual rainfall 

 as the country surrounding the Bay of San Francisco, viz. 

 about 24 inches ; but while in the Franciscan climate this 

 amount of rain falls during one-half of the year, and that the 

 growing season, enabling crops to be grown without irrigation, 

 in Montana the rainfall is distributed over the entire season, 

 so that irrigation is absolutely essential for the successful pro- 

 duction of crops. This so much the more as, while the winter 

 snowfall is very light, the rains of summer are largely torren- 

 tial, running off the surface in muddy floods and giving little 

 time for absorption into the soil. Farther west, in Washing- 

 ton, where grain crops are largely grown without irrigation, 

 the sowing of winter grain is impracticable because the dry 

 summer is immediately followed by the very light snowfall of 

 winter, which falls on dry ground. Fall-sown grain would 

 thus simply lie dormant in the ground through the winter, 

 with great liability to injury from stress of weather in early 

 spring, apart from the depredations of birds and rodents. 

 Hence grain is always sown there in spring only. 



These examples may suffice to show that summary state- 



