History of Forest Ecology 397 



A glimpse into the future of plant ecology points unmistakably 

 to the necessity of a physiological classification of plants. While 

 considerable work has recently been done in habitat relations, 

 only a very small part of it touches this most fundamental 

 aspect of plant ecology. I refer to the physiological point of 

 view emphasized by Schimper (10). The questions involved in 

 relating the facts of the distribution of plants to the factors of 

 the habitat are very imperfectly understood. There is also a 

 great lack of precise knowledge of the various habitat factors and 

 of the physiological responses made by plants to these factors. 

 Until ecologists work out the nature of habitat factors, and until 

 the effect of the factors on the plant has been more closely investi- 

 gated by physiologists, it will be impossible to place ecology on a 

 physiological basis. And when the nature and effect of ecological 

 factors are more fully understood, the artificial classification into 

 geographical, physical, and biological factors will be discarded 

 and a classification based upon the action of the various factors 

 will come into use. In the present state of our ecological 

 knowledge such a physiological classification of plants is im- 

 possible. 



Many schemes have been propounded for the classification of 

 plants according to their gross anatomical and physiological 

 characteristics. Among these classifications of growth forms, life 

 forms, or vegetation types, as they have been variously called, are 

 those of Humboldt, Grisebach, Warming, Raunkiar, and Drude. 

 The recent growth forms of Drude, in which he attempts to 

 classify plants according to their ecological characteristics, is 

 considered by many ecologists the best thus far, and certainly a 

 big step in the right direction. 



III. THE HISTORICAL DEVELOPMENT OF SILVICULTURE 



The development of silviculture has had a great deal in common 

 with that of agriculture. Both are founded upon one or more 

 of the various phases of botanical science and are therefore often 

 spoken of as the two most highly developed branches of applied 

 botany. From earliest times their development and progress have 

 had a great deal in common; even today we look upon them as 

 sister sciences, compare them and speak about the influence each 

 has had upon the other. Both are concerned with the use of the 



