History of Forest Ecology 387 



point of view. But the real beginning of this phase of ecology 

 was made by Wiesner, an Austrian botanist, with his determina- 

 tion of light values in 1896. In 1898, F. E. Clements first began 

 in the United States the study of habitat structure and the de- 

 termination of the various factors by means of instruments. He 

 also developed about this time methods of control experiment in 

 the plant house under definitely measure dififerences of light and 

 water (i. e., he synthetized an artificial habitat). 



Modern ecology is dynamic. It deals largely with the forces 

 of Nature which affect plant life, and it is largely experimental 

 because it is seeking to determine quantitatively the physical fac- 

 tors of the habitat. In this country, Clements has been the chief 

 contributor. He is the author of several ecological works pub- 

 lished between 1904 and 1907 (1, 17, 18, 19, 79). The most im- 

 portant of these is his Research Methods in Ecology, which is 

 an important contribution to the science, not so much in accumu- 

 lating and recording facts as in pointing out the methods, and 

 principles which should be used to secure facts of ecological 

 significance. Cowles, in conjunction with others, is the author 

 (1911) of a textbook on morphological and physiological ecology, 

 in which he treats rather extensively the relation of the habitat 

 to the structure and behavior of the plant. Abroad, English and 

 Danish plant ecologists have been the largest contributors. In 

 1905, H. Solms-Laubach published his very suggestive work; and 

 Warming, in 1909, making use of a large fund of material, gave 

 to the world his book on the Oecology of Plants which is con- 

 sidered one of the best works on the subject. The most recent 

 work of importance covering the subject in a general way is 

 Drude's Die Oekologie der Pflansen, which appeared in 1913. 



The Historical Development of the Study of Vegetation (18) 



The above brief sketch will indicate in a general way the trend 

 of the science. By far the greater part of the history of plant 

 ecology, however, has to do with the development, structure, 

 and classification of plant formations, since this unit is the sine 

 qua non of the science. Some of the earliest observations of 

 ecological significance deal with certain fundamental phenomena 

 of vegetation known as association, invasion, succession, zonation, 

 and alternation. Plants both as individuals and as communities 

 have their peculiar structure, habits, and behavior; both have 



