CONTENTS 



PACK 



23. Mechanism of secretion and excretion 



24. Osmotic pressure in the cell 



25. Specific powers and activities T 47 



26. Importance of the root system ! 49 



27. Absorption of fluids and solids by subaerial organs 158 



28. Importance of the soil . ! ^3 



CHAPTER V 

 THE MECHANISM OF GASEOUS EXCHANGE 



29. General 176 



30. Passage of gases through cells and cell- walls 183 



31. Communications of the aeriferous system with the external world . . . 188 



32. Movements and pressure of the internal gases 199 



CHAPTER VI 

 MOVEMENTS OF WATER 



33. General view 207 



PART I. TRANSFERENCE OF WATER. 



34. Conveyance of water in transpiring plants 210 



35. Conducting channels 213 



36. Mechanism of water transport 220 



37. Relation between transpiration and absorption of water 228 



PART II. EXCRETION OF WATER VAPOUR. 



38. Influence of specific peculiarities on transpiration ...... 234 



39. external conditions 245 



40. Transpiration under normal conditions ........ 249 



PART III. EXCRKTION OF FLUID WATER. 



41. General view 252 



42. Bleeding of injured plants 253 



43. Amount and pressure 257 



44. Influence of external conditions . 263 



45. Periodicity of bleeding 264 



46. Mechanism of active exudation 268 



47. Excretion of water from uninjured plants 272 



48. from water-pores 278 



49- of nectar 281 



CHAPTER VII 



THE FOOD OF PLANTS 



PART I. GENERAL VIEW. 



50. Nutritive metabolism 287 



51. Circulation of food materials in organic world 297 



