Water Requirements 127 



practically the same as when one third as much water 

 was supplied. 



Date-palm. - - In the Saharan region of northern Africa, 

 where the date-palm is most extensively grown, the pre- 

 cipitation is commonly less than ten inches. Moreover, 

 during the growing season the air is intensely dry, and 

 evaporation reaches a maximum. Under such conditions, 

 and assuming no subterranean water-supply, it has been 

 estimated l that this plant (a tree of medium size) requires 

 a maximum of from 100 to 190 gallons of water per day 

 during at least four months, making a total of from 3^ to 

 4J feet of irrigation-water annually. 



69. Potted plants and water supply. - - Potted plants 

 possess such diverse water requirements that it is often 

 difficult for the amateur grower to arrive at any satisfac- 

 tory principles for watering. First of all, it is clear that 

 the amount given should be in proportion to the water- 

 loss. Plants in a dry room or greenhouse may require 

 many times as much water as those in a shaded green- 

 house full of vegetation, with air fairly saturated. Most 

 potted plants are quickly injured or killed by constant 

 saturation, and the practice of saturating the pot and filling 

 the jardiniere around it is soon fatal; for with the usual 

 amount of organic matter in the soil the exclusion of air 

 to this extent is harmful both directly and indirectly. 



Viewing this matter in the light of such experimental 

 work as has been undertaken, it seems that during the 

 growing season a constant, favorable supply of water from 

 below is most desirable. This, of course, is not always 



1 Swingle, W. T., " The Date-palm." Bur. Plant Ind., U. S. Dept. 

 Agl., Bui. 53 (cf. pp. 47-48), 1900. 



