LIST OF TEXT ILLUSTRATIONS 



Figure 1. — Trihydrol molecule as pictured by Sutherland 4 



Figure 2. — The tetrahedral water molecule of Pennycuick 8 



Figure 3. — The polar water chain 9 



Figure 4. — The hexagonal ring structure of water, comparable with the crystal 



structure of ice 9 



Figure 5. — Diagram indicating the self-ionization of a water chain 10 



Figure 6. — Electronic distribution in the simple water molecule 11 



Figure 7. — The crystal lattice of ice as pictured by Bernal and Fowler ... 12 

 Figure 8. — Diagrammatic illustration of the shift from the hexagonal lattice of ice 



to a closer packed structure for water 15 



Figure 9. — Typical vapor pressure-water content curves for sand and clay showing 



the values of the permanent wilting percentage and field capacity for each . . 23 

 Figure 10. — Curves showing the relation between moisture content and relative 



humidity of the atmosphere surrounding cotton, and spruce wood 24 



Figure 11. — Apparatus for demonstrating differential diffusion of gases ... 45 

 Figure 12. — Diagram showing the relations between attractive and repulsive forces 



between molecules 47 



Figure 13. — Diagram showing the relations of partial and total vapor pressures of 



solutions according to Raoult's Law 48 



Figure 14. — Apparatus useful in analysing problems of osmosis 49 



Figure 15. — Relations among osmotic pressure, diffusion pressure deficit, and turgor 



pressure for an ideal osmometer 50 



Figure 16. — Calculated and observed values of osmotic pressures of cane sugar 



solutions ^'* 



Figure 17. — Several types of parenchyma cells found in plants 60 



Figure 18. — Protein structure pictured by Frey-Wyssling 67 



Figure 19. — A diagrammatic presentation of the relations among osmotic pressure, 



diffusion pressure deficit, and turgor pressure as applied to plant cells . . . 73 



Figure 20. — Three forms of TP-volume curves for plant cells 74 



Figure 21. — The relation between concentration of plasmolyzing solution and degree 



of plasmolysis 86 



Figure 22. — Plasmolysis types as illustrated by Strugger 87 



Figure 23. — Onion epidermal cell showing cap plasmolysis 88 



Figure 24. — Tonoplast plasmolysis of onion epidermis 88 



Figure 25. — Vacuole contraction in a cell of the fruit flesh of Ligustrum vulgare 89 

 Figure 26. — Vacuole contraction in an onion epidermal cell having the vacuole strong- 

 ly stained with neutral red 89 



Figure 27. — Vacuole contraction as shown by leaf cells of Elodea canadensis after 



staining with neutral red 90 



Figure 28. — Press cylinder outfit used to express small amounts of sap from plant 



tissue 91 



Figure 29. — Construction of cryoscopic apparatus 92 



Figure 30. — Calibration curve for the apparatus shown in figure 29 94 



Figure 31. — Freezing curve constructed according to recommendations of Mair, 



Glasgow, and Rossini 95 



Figure 32. — The Barger Halket method for determining the osmotic pressure of 



plant sap 96 



Figure ZZ. — Osmotic pressure determination by the method of Ursprung and 



Blum 96 



Figure 34 A. — Diffusion pressure deficit values determined by the volume method 102 

 Figure 34 B. — Diffusion pressure deficit values determined by the weight method 103 

 Figure 35. — Diagrammatic illustration of water movement along a gradient of 



DPD 109 



Figure 36. — Osmotic pressure values of leaf cells of Bergenia cordifolia . . .114 

 Figure 37. — Seasonal variations in the dry matter content, inexpressible water, and 



water expressed as sap after different treatment of leaves of Pinus rigida . . 121 



