CONTENTS. 
PAGE 
Introduction 5 
Review of previous work — 
Older view of the importance of the hygroscopicity of soils 8 
Recognition of the falsity of the older view 10 
Studies of the hygroscopie coefficient by Hilgard and Loughridge. . 12 
Later studies on the nonavailable water and on the relative 
hygroscopicity of soils 14 
Previous studies by the writer 16 
Recent studies by Briggs and Shantz IS 
General description of the experiments 21 
Soils used 21 
Plants grown 21 
Greenhouse used 21 
Determination of the soil moisture 28 
Free water 30 
Wilting coefficient 31 
Determination of the dry matter of the crops 32 
Preliminary experiment 32 
Growth of wheat on semi-arid soil compared with that on humid soil. 
Experiment of 1909 33 
Summary of experiment 44 
Growth of crop plants with different amounts of water in the sub- 
soil. Experiment of 1910 7S 45 
Filling the cylinders 48 
Separation of roots from the subsoil 49 
Cylinders without plants 5L 
Red Fife wheat 52 
Cylinder with no free water in the subsoil 58 
Cylinders with 4 per cent free water in the subsoil 60 
Cylinder with 7 per cent free water in the subsoil 61 
Cylinder with 12 per cent free water in the subsoil 61 
Two cylinders with moister soil near the surface 61 
Kubanka wheat 62 
Cylinder with no free water in the subsoil 65 
Cylinder with 4 per cent free water in the subsoil 65 
Cylinder with 8 per cent free water in the subsoil 65 
Cylinder with 12 per cent free water in the subsoil 67 
Two cylinders with moister soil near the surface 68 
Milo 68 
Cylinder with no free water in the subsoil 69 
Cylinder with 4 per cent free water in the subsoil 69 
Cylinder with 8 per cent free water in the subsoil 69 
Cylinder with 12 per cent free water in the subsoil 70 
Two cylinders with moister soil near the surface 71 
Mexican beans 74 
Summary of experiment of 1910 76 
