CONTENTS. 



PAGE. 



Preface jX 



Part I. The Vegetation of the United States. 

 Introduction: 



I. The distribution of vegetation in general, as related to climatic conditions . . 3 



II. Study of the distribution of individual species 7 



III. Manifold operation of environmental conditions 12 



IV. Growth-forms of pljwits 14 



Table 1. — Analysis of Drude's criteria for distinguishing 



giowth-forms 19 



V. Plant communities 22 



VI. DeHmitation of vegetational areas 26 



Distribution of Vegetation in the United States: 



I. Methods used in securing and presenting the distributional data 29 



II. Leading vegetation types of the United States and their geographical areas 32 



III. Distributional areas of conformic groups of plants 46 



IV. Distributional areas of selected individual species 64 



Part II. Environmental Conditions. 



Introduction 95 



General Influence of the Environment on Plant Life: 



I. External and internal conditions and plant activity 97 



II. Theory of physiological Umits 99 



III. Relation of plant distribution to the physiological limits of the various 



developmental phases 101 



IV. Genetic continuity of protoplasm and its cyclic activities, in connection 



with problems of distribution 104 



Chief Environmental Conditions and the General Nature of Their 

 Effects Upon Plants: 



1. General classification of environmental factors 109 



II. Moisture: 



1. Water requirement within the plant Ill 



2. Supply of water to the plant 115 



3. Relations between water-requirement and water-supply 119 



III. Temperature: 



1. Temperature requirement within the plant 126 



2. The relation of temperature within the plant to conditions of 



environment 128 



3. The dui-ation aspect of the temperature relation 131 



IV. Light: 



1. General nature of light 135 



2. Effect of light upon plants 136 



3. Duration aspect of light relation of ordinary plants 137 



V. Chemical conditions: 



1. Requirement of material within the plant 138 



2. Material exchanges between the plant and its surroundings 139 



3. Chemical environment in nature 141 



4. Duration aspect of chemical conditions 143 



VI. Mechanical conditions: 



1. General considerations 143 



2. Destructive influences of mechanical conditions 144 



3. Favorable influences of mechanical conditions 145 



VII. Interrelations of the environmental conditions 146 



VIII. Experimental determination of relations between plant activity and 



environmental conditions 147 



m 



I biri<i 



