TABLE OF CONTENTS. XV 



CHAPTER XXXVIII. 



PAGE 



ECONOMIC OR USEFUL PLANTS 422 



Monocotyledons 422 



Dicotyledons 433 



CHAPTER XXXIX. 



RELATION OF PLANTS TO ENVIRONMENT OR ECOLOGY ....... 451 



I. Factors influencing vegetative type 451 



II. Vegetation types and structures 455 



CHAPTER XL. 



MIGRATION AND DISTRIBUTION OF PLANTS 461 



I. Methods and causes of plant migration 462 



II. Barriers to plant migration 467 



CHAPTER XLI. 



PLANT SOCIETIES 469 



Forest societies 470 



Other plant societies 476 



CHAPTER XLII. 

 SOME PRINCIPLES OF PLANT EVOLUTION . . . 485 



CHAPTER XLIII. 



SOME PRINCIPLES OF PLANT BREEDING . 494 



I. The improvement of existing varieties 495 



II. The production of new varieties 497 



GLOSSARY 509 



INDEX 527 



