xiv TABLE OF CONTENTS. 



CHAPTER XLVIII. 



PAGE 



LAWS AND LIMITS OF PLANT MIGRATION 497 



I. Relation of Plants to Earth's Surface as a Whole. . 49 8 



II. Life Regions, Zones, and Areas 500 



III. Methods and Causes of Plant Migration 506 



CHAPTER XLIX. 



PLANT FORMATIONS 515 



I. Climatic Formations 515 



II. Edaphic Formations 518 



III. Aquatic Formations 521 



IV. Culture Formations 521 



V. Principal and Individual Formations 522 



CHAPTER L. 



FOREST SOCIETIES 529 



I. General Character of Forest Societies 529 



II. Boreal Forests 534 



III. Austral Forests 535 



IV. Tropical Forests 541 



V. Relation of Forests to Rainfall 546 



VI. Forest Regeneration and Protection 548 



CHAPTER LI. 



THE PRAIRIE AND PLAINS SOCIETIES 556 



I. Grassland Formations 556 



II. Prairie Formations 557 



III. The Plains Formations 559 



IV. Edaphic Formations in the Prairie Region 560 



CHAPTER LII. 



DESERT PLANT SOCIETIES 565 



I. Characters of True Desert Plants 565 



II. The Sonora-Nevada Desert 568 



III. Other Desert Regions 573 



CHAPTER LIII. 



ARCTIC AND ALPINE PLANT SOCIETIES S7 6 



I. Arctic Plant Societies 57 6 



II. Alpine Plant Societies 5 g 2 



