TABLE OF CONTENTS XV 



CHAPTER XXXVI. 



PAGE 



ECONOMIC OR USEFUL PLANTS 392 



Monocotyledons 392 



Dicotyledons 402 



CHAPTER XXXVII. 



RELATION OF PLANTS TO ENVIRONMENT OR ECOLOGY 421 



I. Factors influencing vegetative type 421 



II. Vegetation types and structures 425 



CHAPTER XXXVIII. 



MIGRATION AND DISTRIBUTION OF PLANTS 431 



I. Methods and causes of plant migration 432 



II. Barriers to plant migration 437 



CHAPTER XXXIX. 



PLANT SOCIETIES 439 



Forest societies 440 



Other plant societies 446 



CHAPTER XL. 



SOME PRINCIPLES OF PLANT EVOLUTION 455 



CHAPTER XLI. 



SOME PRINCIPLES OF PLANT BREEDING 464 



I. The improvement of existing varieties 465 



II. The production of new varieties .467 



INDEX 479 



