vi Contents. 



CHAPTER IV. 



PHYSICAL NATURE OF Soil*. 



PAGE. 



TBXTURE OF SOIL 108 



Size of soil grains, p. 108 ; Size of soil kernels, p. 110. 



PORK SPACE IN SOIL Ill 



Determines maximum water capacity, p. 114; Influences rate of 

 percolation, p. 115 ; Method of measuring, p. 115 ; Largest possi- 

 ble, p. 116. 



INTERNAL SURFACE OF SOILS 118 



Amount per gram and sq. ft., p. 118 ; Determination, p. 119. 



EFFECTIVE DIAMETER OF SOIL GRAINS 121 



Method of determination, p. 121 ; Flow of fluids computed from, 



p. 123 ; surface computed from, p. 124. 

 WEIGHT OF SOILS 127 



CHAPTER V. 

 SOIL MOISTURE. 



CONDITIONS OF SOIL MOISTURE 129 



Gravitational, p. 329; Capillary, p. 130; Hygroscopic, p. 130. 



WATEB CONTENT OF SOILS 131 



Ways of expressing, p. 131 ; Maximum capacity of field soils, p. 

 131 ; Capillary capacity, p. 132 ; Influence of distance above 

 standing water on capacity, p. 134. 



SOIL MOISTURE AVAILABLE TO CROPS 135 



Soils which yield moisture most completely, p. 136 ; Relation of 

 thickness of moisture film to per cent, of water, p. 137 ; Af- 

 fected by jointed structure, p. 138; Increased by open struc- 

 ture, p. 138 ; By drainage, p. 139. 



AMOUNT OF WATBH REQUIRED BY CROPS 139 



For different yields of wheat, p. 140 ; Least amount for different 

 crops, p. 141. 



CHAPTER VI. 

 PHYSICS OF PLANT BREATHING AND ROOT ACTION. 



MECHANISM AND METHOD OF TRANSPIRATION 142 



Breathing of plants and animals, p. 142 ; Respiratory organs In 

 plants, p. 142 ; Breathing pores, p. 143 ; chlorophyll cells, p. 

 143 ; Guard cells, p. 143 ; Their action, p. 144 ; Loss of water 

 through, p. 145. 



STRUCTURE AND MODE OF ROOT ACTION 145 



Functions of roots, p. 145 ; Absorbing portion, p. 146 ; structure 

 of root hairs, p. 147 ; Relation to soil grains, p. 147 ; Method of 

 gathering water, p. 147 ; Advance through soil, p. 148 ; Ex- 

 tent of root development, p. 150; Total root of plants, p. 157. 



