214 



PHYSICAL ENVIRONMENT 



nutrient supply varies with the kind of soil ; and the supply 

 determines to a large extent the character of the individual 

 plant. On poor soils plants are small; on rich soils they are 

 large. The difference between poor and good yields of wheat, 

 or any other crop, is largely a question of soil-fertility. 

 The farmer reinforces his poor soils by the addition of ferti- 

 lizers, in order to make his plants vary into larger or more 

 productive individuals. 



380. One-sided holly tree growing near the ocean. New Jersey. 



373. The moisture-content of the soil exerts a marked 

 influence on plants. We have found (157) that a large 

 part of the plant-substance is water. The water is not only 

 itself food for plants, but it carries nutrients into the plant 

 and transports them from tissue to tissue. However rich 

 a soil may be in mineral nutrients, it is inert if it contains 

 no moisture. The character of the plant is often determined 

 more by the moisture in the soil than by all the other soil 



