I 



CHAPTER V 

 THE SOIL 



I. The Physical Properties of the Soil. Water capacity. Conveyance of water 

 by capillarity. Permeability of various kinds of soil. 2. The Chemical Properties of 

 Soils. Correlations of physical and chemical properties. Effects of solutions on the 

 absorption of water by plants. Poisonous nature of concentrated solutions. Protective 

 mechanism of plants against increasing concentration of saline solutions in the cells. 

 Various actions of salts on the structure of plants. 3. Sodium Chloride, i. Presence and 

 Function of Sodium Chloride in Plants. Influence of sodium chloride on the structure of 

 plants. Xerophilous character of halophytes. Influence of sodium chloride on the pro- 

 duction of proteids. Its influence on the structure of fresh-water Algae, ii. Halophytes. 

 Predilection for salt. Distribution of halophytes among the families of plants. Origin 

 of the halophilous mode of life. Inability to withstand competition inland. 4. Other 

 easily soluble Salts. Alum : the solfataras. Saltpetre. 5. Serpentine. Plants growing 

 on serpentine. 6. Calamine. Calamine-plants. 7. Calcium Carbonate, i. Action of 

 Calcium Carbonate on the Metabolism and Structure of Plants. Poisonous effects on 

 many plants. Power of accommodation to a calcareous soil. Experiments and observations 

 by Bonnier and others. Nature of the influence of lime on metabolism. Experimental 

 cultures by Fliche and Grandeau. ii. Character of the Flora on Calcareous Soil. Calci- 

 philous plants. Calciphobous or silicicolous plants. Instability of the relations of plants 

 towards lime. Thurmann's physical theory. Its refutation. Explanation of the difference 

 between calcicolous and silicicolous floras, and of their instability. Dissimilar relations 

 to lime of closely allied species. Parallel forms on soils rich and poor in lime. Nageli's 

 theory. 8. Humus, i. The Chemistry and Physics of Humus. Ash-constituents. Acid 

 humus and mild humus. Leaf-mould and peat. ii. The Mycorhiza. Endotrophic and 

 ectotrophicmycorhiza. Thismia Aseroe according to P. Groom. Saprophytes, m. Chemical 

 Differences in Humus and the resulting Flora. Dissimilar nature of the flora on different 

 kinds of humus. Great exclusiveness of certain species of plants. Plants growing on 

 animal humus. 9. Living Substrata : Parasites. Dependence on the chemical nature 

 of the substratum. 



1. THE PHYSICAL PROPERTIES OF THE SOIL. 



The physical properties of the soil 1 that are most important to plant-life 

 depend not so much on the formerly over-estimated forces of cohesion, 

 which offer a more or less considerable resistance to the growth of the 

 subterranean members of plants, as on the forces of adhesion and capillarity 

 which regulate the amount of water and air in the soil. At different spots 

 in one region with uniform rainfall the soil exhibits the numerous stages 

 between a dry and a wet condition, according to its water-capacity, its 



1 See especially Ad. Mayer, op. cit. 

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