xvi CONTENTS 



IX. THE POWER OR ENERGY OF THE PLANT 



PAGE 



218. Energy of the plant 182 



219. Sources of energy 182 



220. Sunlight as a source of energy 183 



221. Chemical compounds as a source of energy . . . 183 



222. Physical attraction as a source of energy . . . 184 



223. Release of energy 184 



224. Respiration, or breathing 184 



225. Changes in the air produced by breathing . . . 185 



226. Plants by day and by night 186 



227. Relation of the living world and the atmosphere . . 187 



228. Energy of physical attraction 189 



229. Outward work accomplished by physical attraction . 190 



X. RELATIONS OF PLANTS TO EACH OTHER, AND THE 

 PLACE IN WHICH THEY LIVE 



230. Societies and communities 191 



231. Plant societies 192 



232. Foundations of society 192 



233. Communities change 193 



234. Water and plants 194 



235. Temperature and plants 194 



236. The soil and plants 195 



237. Light and plants 195 



238. Wind and plants 196 



239. Forests 196 



240. Relations of members of the forest 201 



241. Time of blooming 201 



242. Seasonal activity 202 



243. Families and species in a community .... 204 



244. Meadows 205 



245. Rock societies 206 



246. Pond societies ......... 207 



