CHARACTERISTICS OF SOILS 23 



Only a brief outline can be given, in this discussion, of 

 the way in which this feeding process takes place. This 

 general statement is sufficient to indicate the general 

 part that water plays in the work. 



34. Service of water within the plant. Within the 

 plant, the water continues to be the carrier of the food. 

 It delivers its load to the leaves. There the food is 

 elaborated and much of the water is dismissed into the 

 air by way of openings in the leaf walls. Some of the 

 water is still retained, a part of it to be used by. the plant 

 as food, and the remainder to continue its service as 

 carrier ; but its burden now is elaborated food, and its 

 function is to distribute this food to the parts requiring it 

 for growth or storage. Some of it is carried to the stems, 

 some to the leaves, some to the maturing seeds, and some 

 even to the extreme ends of the roots. 



35. Quantities of water required by crops. Most of 

 the plant-foods are only slightly soluble in water ; that is, 

 a large quantity of water is required to dissolve a small 

 quantity of food. Storer states that, in ordinary soils, 

 a thousand pounds of water can dissolve from one half 

 to one and one half pounds of mixed organic and mineral 

 matters. 1 For this and other reasons, large quantities of 

 water are required to produce a good crop yield. When 

 the water supply is short, the crop yields are necessarily 

 lowered. Table V is a modification from King and has 

 been prepared chiefly to show the least possible amount 

 of water that may be expected to produce the yields 

 indicated in the first column of the table. The required 

 amounts are expressed both in tons and in inches of 

 rainfall. These amounts include the losses by evapora- 

 tion from the surface of the ground in the growing season, 



1 Storer, Agriculture, Vol. I, p. 285. 



