IRRIGATION PRACTICE AND HIGHWAYS 315 



(b) dissimilar soils require different amounts of wa- 

 ter to produce satisfactory growth of plants; (c) 

 local climates, chiefly because of the degrees of thirst 

 in the air, require different amounts of water and 

 unlike intervals between applications, for the same 

 crop; ( d) the size, quality and commercial value of 

 all crops is dependent on adequate moisture accord- 

 ing to the needs of particular plants to discharge 

 their agricultural functions. 



The disagreement among early Californians about 

 the desirability of irrigation arose largely from their 

 lack of understanding of the relation between the 

 highest thrift of the plant and the quantity and qual- 

 ity of its product. It required a number of years of 

 experience to reach a general appreciation of what 

 a plant will do under certain circumstances. Then 

 came the perception that irrigation improvements, 

 under all conditions which require them, consist of 

 assuring the plant the constant and adequate water 

 supply which favors full development and produc- 

 tiveness. It appears, then, that the successful grower 

 must know the needs of his plants, the water capac- 

 ity of his soil and the rate of use by the plant as 

 well as the rate of waste at different times of the year, 

 and depend on rainfall alone or on rainfall supple- 

 mented by irrigation or by irrigation alone, according 

 as either form of practice is required. 



A concrete illustration of the behavior of a plant 

 under various growing conditions may be drawn from 

 the possible performances of the peach, which ranks 

 next to the prune as the most largely grown decidu- 



