102 Elementary Principles of Agriculture 



and fungi. Weak, poorly nourished plants are not fruit- 

 ful. Healthy plants have large leaves. Large leaves 

 indicate vigor. The rank-growing weeds have large 

 leaves. Increasing the amount of leaf surface is increas- 

 ing the capacity of the plant to manufacture plant 

 substance. 



150. Relation of Leaf Surface to Soil Moisture. The 

 total leaf surface on a plant may be several times the 

 total ground surface shaded by the plant. If evapora- 

 tion is increased by the winds or high temperatures, it 

 may happen that the supply of soil moisture may become 

 exhausted and the plant suffer. Soils covered with plants 

 lose their moisture faster than if they are bare or fallow. 

 In regions of slight rainfall, therefore, it often becomes 

 desirable to reduce the number of plants to prevent too 

 great a draft on the stores of soil moisture. This is an 

 additional reason for leaving space between the indi- 

 vidual plants in a crop. (See f 102.) 



151. How Far Apart Should Plants Be Grown? Where 

 the value of the crop depends on the perfect develop- 

 ment of the individual plant, or some special part, such 

 as the leaves, flowers, fruits, stems, or roots, sufficient 

 space should be allowed that adjacent plants will not 

 interfere with each other. However, the value of the 

 crop often depends more on the total weight of the 

 harvest than on the quality of the individual plants. 

 In such cases, the loss from a limited amount of shade 

 will be more than made up by the increased number 

 of plants, as in the case of the grain crops. Again, the 

 fertility of the land also affects the size of the plants, 

 and, of course, the space which each should be allowed. 

 Often the use for which the crop is intended must be 

 considered, as, for instance, in the case of sorghum grown 



