66 FORREST SHREVE 



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Students of vegetation are using at present a natural system 

 of classification of types of vegetation, distinguishing evergreen 

 and deciduous forest, grassland and savanna, heath and moor. 

 Back of the patent dissimilarity of these communities lies the 

 unlikeness of their dominant plants, and behind this unlikeness 

 lie the anatomical-physiological differences between these plants. 

 To learn more about the physiology of individual dominant 

 species in the evergreen forest, the grassland or the heath will 

 give us a more precise knowledge of the life-forms to which they 

 belong, and will aid us in the investigation of the factors which 

 limit the physically controlled species of these communities. A 

 better understanding of the life-forms will give us a sounder basis 

 for the distinguishing of types of vegetation. There is no ihi- 

 portance in asking whether the nearly pure stands of CoviUea 

 which occur from the Mojave Desert to Zacatecas are desert, 

 bush-steppe or chaparral. We should have for them something 

 more than a casual examination, a personal opinion, and a 

 colloquial or polysjdlabic name. We can have it only by learning 

 more about the physiology of CoviUea. Such knowledge might 

 elucidate the known distributional facts about some other similar 

 shrubs, or it might emphasise the importance of studying the 

 other shrubs as well. 



The whole group of problems in the general and local dis- 

 tribution of physically controlled plants resolves itself into a 

 painstaking study of the physiology of the plants and the physics 

 and chemistry of the environment. We do not need the methods 

 of ph3^sics and chemistry, as is so often said. We need training 

 in physics and chemistry and we need methods of our own. 



The subject of plant geography, considered in its widest sense, 

 presents a field of enormous width, takings its facts from tax- 

 onomy, learning as much of the past as it can from paleobotany, 

 using the methods and demanding the knowledge of the clima- 

 tologist, the geologist, the physiographer, and the soil physicist, 

 and carrying its ultimate problems to the physiological laboratory 

 or to the specially equipped field station. The attack upon this 

 wide field is at present being made upon its extreme edges. Those 

 who form the attacking force are either advancing in the geo- 



