Periodical Literature 327 



This experiment proves conclusively the influence of exterior 

 conditions on growth. 



Was wissen wir vom Wachslum der Bdume. Schweizerische Zeitschrift fur 

 Forstwesen, January-February, 1916, pp. 1-12. 



SOIL, WATER AND CLIMATE 



The importance of the chemistry of col- 



Importance loids with reference to soil conditions and 



of the use of soils in forestry and agriculture 



Colloids is brought out by Prof. Dr. Rohland in the 



in following manner: 



Forestry Clay and clayey soils, according to the 



author, as well as the humus and peat soils, 

 owe their characteristics to the colloid materials contained in 

 them; these soils owe also their fertility to the colloids. Sandy, 

 crystalloid soils are free from colloids and, therefore, possess less 

 water capacity than the former and less absorption of water 

 vapor. 



One may conceive the colloids as a tissue of fine mesh in which 

 the water can adhere as in a sponge. In this water the nutritive 

 salts are found in solution, as well as the crystalloids, and owing 

 to this sponge action are not as readily leached out as in a sandy 

 soil. There are also certain chemical exchange processes taking 

 place in the colloid soils according to the laws of equivalency, 

 e. g., calcium may be displaced by a corresponding amount of 

 potassium, which is much more valuable in the nutrition of plants. 

 Similarly, the magnesium salts, important in the formation of 

 chlorophyll, can displace the calcium salts. Hence the applica- 

 tion of gypsum is effective only when such soluble salts are pres- 

 ent, which they are in colloid soils ; and so other fertilizers, such 

 as superphosphates, plaster, marl, depend in their effectiveness on 

 the presence of exchangeable salts. 



Alkali and alkaline earths applied to clay soils effect flocculation 

 of their colloid contents with concomitant volume increase; the 

 clayey constituents experience a colloid-chemical change of con- 

 stitution with consequent loosening of the soil. 



If, however, clay and clayey or humus soils are dried, they 

 give up the colloid-chemically absorbed water, and they lose some- 

 what the capacity of taking up water; and, if repeatedly dried, 



