SOIL FOR GREENHOUSES 183 



In considering the amounts of organic matter present 

 in soils, the same authorities state : "In general, arid 

 soils contain less organic matter than soils of humid 

 regions ; those of cold climates more than those of warm 

 climates. The soils of the northern states and Canada 

 are very generally quite dark colored, while those of the 

 southern states under similar treatment are much lighter 

 colored, due to difference in organic contents. Wet soils 

 contain more than dry soils, and clay soils more than 

 sandy soils." 



Both the chemical and physical effect of organic matter 

 on the soil are of great value to the plant-grower. As be- 

 fore stated, soils deficient in organic matter are lifeless. 

 Organic matter renders clay soils lighter in character and 

 more thoroughly aerated ; it makes sandy soils more reten- 

 tive of moisture, and better suited for healthy root action ; 

 it adds color to sandy soils, rendering them darker, thus 

 increasing their power to absorb the heat of the sun's rays. 

 From the chemical viewpoint, the presence of organic 

 matter increases the direct food materials, and the for- 

 mation of organic acids renders soluble many insoluble 

 mineral elements in the soil, thus making them available 

 for plant food. 



154. Sanitary relations of soils. In an excellent 

 paper l on " Soil Problems of the Florist," E. O. Fippin 

 states as follows : " I cannot fail to dwell upon the sani- 

 tary relations of the soil. It is now very well known that 

 the whole question of fertility is not comprised within 

 those positive processes of supplying plant-food or other 

 factors for growth. With all these well supplied, plants 

 may still fail because of the existence of some inhibiting 



1 A paper read before the New York State Federation of 

 Floral Clubs at the winter meeting at Ithaca, N.Y., in 1914. 



