INDEX. 



253 



Sources of hydrogen in plant tissue, 



23. 



of mineral matters in plant 

 tissues, 23. 



Species, domestic and domesticated, 

 33. 



Springs, source of water discharged 

 by, 109. 



Sprouting vegetation, influence of, 

 on disintegration of rocks, 53. 



St. Helena, Lyell on the destruc- 

 tion of its forests, 87. 



Struggle for existence in the vege- 

 table world, 61. 



Subsoil, definition of, 60. 



Sunshine, influence of, in germina- 

 tion of seeds of plants, 21. 



Surface drainage, definition of, 

 110. 



Surface, influence of, on rapidity 

 of evaporation, 91. 



T. 



Temperature of air, influence of, on 

 rapidity of evaporation, 91. 

 of equatorial and polar regions, 

 how balance is preserved be- 

 tween, 164, 165. 

 Tree-planting, 155 to 159. 



when advisable, 27. 

 Trees, conditions necessary for 



growth of, 42 to 47. 

 Tree-sowing, 157. 

 Torrents, influence of, on destruc- 

 tion of forests, 58. 

 Tropical flora, why different from 

 temperate or arctic flora, 



26. 



rains, how caused, 102. 

 regions, forests of, 46. 



Tropical vegetation, Guyot's de- 

 scription of, 28, 29, 30. 

 Tyndall, John, extract from " Heat 

 as a Mode of Motion," 98, 105, 

 134. 

 Typographer beetle, destruction of 



forests by, 75. 

 Hough on, 76, 77. 



U. 



Underground drainage, definition 

 of, 110. 



V. 



Vacuum, influence of, on germina- 

 tion of seeds, 40. 

 Vapor, earth's ocean of, 90 to 97. 

 of air, chilling necessary for 

 precipitation of, 

 100. 



influence of, on econ- 

 omy of the earth, 

 93, 94. 

 Vegetable fibre, source of carbon 



in, 22. 



mould or humus, 50. 

 world, struggle for existence 



in, 61. 



Vegetation, agency of, in prevent- 

 ing loss of soil, 88. 

 Velocity of wind, influence of, on 



rapidity of evaporation, 92. 

 Volta's electrical theory of hail, 

 149, 150. 



W. 



Wadys in the Sahara Desert, 34. 

 Water or moisture, necessity of, for 

 plant growth, 24. 



22 



