xvi OUTLINE AND TABLE OF CONTENTS 



PAGE 



III. Mineral substances absorbed by plants 279 



a. Substances found in ash of plants (143). 



b. Amounts of plant-food material removed by crops(144). 



c. Amounts of plant-food material contained in soils(145). 



d. Possible exhaustion of mineral nutrients (146). 



IV. Acquisition of nutritive salts by agricultural plants. . . . 286 



a. Selective absorption (147). 



b. Relation between root-hairs and soil-particles (148). 



c. Absorptive power of different crops (149). 



1. Extent of absorbing system (150). 



2. Osmotic activity (151). 



3. Cereal crops (152). 



4. Grass crops (153). 



5. Leguminous crops (154). 



6. Root crops (155). 



7. Vegetables (156). 



8. Fruits (157). 



V. Absorption by the soil of substances in solution 297 



a. Substitution of bases (158). 



b. Time required for absorption (159). 



c. Insolubility of certain absorbed substances (160). 



d. Influence of size of particles (161). 



e. Causes of absorption (162). 



1. Zeolites (163). 



2. Other absorbents (164). 

 /. Adsorption (165). 



g. Occlusion (166). 



h. Adsorption as related to drainage (167). 



1. Substances usually carried in drainage water (168). 



2. Drainage records at Rothamsted (169). 



i. Relation of absorptive capacity to productiveness(170). 



VI. Alkali soils 307 



a. Composition of alkali salts (171). 



b. White and black alkali (174). 



c. Effect of alkali on crops (173). 



1. Direct effect (174). 



2. Indirect effect (175). 



