134 POMOLOGY 



and conserve moisture. If a stony soil is selected, and it 

 frequently is very satisfactory, it should be fertile and 

 productive. 



117. Chemical nature of fruit soils. — It is generally 

 agreed that the mechanical make-up or texture of the soil 

 is even more important than its fertility, since it is more 

 difficult to change materially. However, it is a mistaken 

 notion that the poorest soils should be selected for fruit- 

 trees. This is true in spite of the fact that some kinds of 

 fruit can usually be grown on the poorer soils with more 

 success than most agricultural crops. It must also be rec- 

 ognized that it is not entirely the percentage of mineral ele- 

 ments m the soil in available form that makes for its fer- 

 tility, but of great importance are the organic or humus 

 content and its consequent soil flora together with a proper 

 water relation and the absence of toxic materials or "unsan- 

 itary" conditions. 



A chemical analysis of agricultural soils shows that the 

 following elements are usually present: Silicon, aluminum, 

 iron, phosphorus, calcium, magnesium, sodium, and potas- 

 sium. Sulfur and chlorine are also found in small quan- 

 tities. The nitrogen of the soil, which is so important to 

 plant growth, is almost entirely in the form of organic mat- 

 ter, although the soil-air contains small amounts of the at- 

 mospheric nitrogen and also more or less ammonia. Nitro- 

 gen occurs in mineral form in some places or is obtained by 

 manufacture and purchased as nitrate of soda, potassium 

 nitrate, and sulfate of anmionia for agricultural purposes. 

 If the silicon, alummum, and sodium are eliminated as un- 

 essential plant-foods, it leaves but 15 per cent of the soil as 

 the source of the mineral constitutents of plants. 



118. Soil color. — While the question of soil color may 

 be over-emphasized, nevertheless certain characteristics 

 are correlated with it. A dark color usually indicates the 



