CONTENTS xiii 



PAGE 



241. The Community 227 



242. The Family 228 



Experiment 60. The Structure of a Formation 229 



243. Layers 229 



Experiment 61. Layered Formations 230 



244. Classification 230 



245. Classification by Habitats 231 



246. Types of Formations 232 



247. Developmental or Physiographic Classification 233 



248. Regional Classification 234 



249. Open and Closed Formations 235 



250. Mixed Formations 235 



Experiment 62. Comparison of Formations 236 



CHAPTER XII 

 AGGREGATION AND MIGRATION 



251. Aggregation 237 



252. Simple Aggregation 237 



253. Mixed Aggregation 239 



Experiment 63. Study of Families and Communities 240 



254. Migration 240 



255. MobiUty 241 



256. Organs of Dissemination 241 



257. Modifications for Migration 242 



258. Influence of Seed Production 243 



259. Position of Disseminules 244 



260. The Agents of Migration 244 



201. The Work of Migration Agents 248 



Experiment 64- Modifications for Migration 249 



262. The Direction of Migration 249 



Experiment 65. Amount and Direction of Migration 250 



CHAPTER XIII 

 COMPETITION AND ECESIS 



263. Competition 251 



264. The Struggle for Existence 251 



265. The Nature of Competition 252 



266. The Factors Involved 253 



267. Competition for Water and Light 253 



268. Competition between Parents and Offspring 254 



269. Competition between Different Species 255 



270. Influence of Vegetation Form and Habitat Form 256 



271. The Effect of Position ^56 



