History of Forest Ecology 395 



Transeau, Fuller, Shantz, Shreve, Pool, and others have con- 

 tributde to this field, while in England such men as Tansley, 

 Oliver, Crump, Moss, and Yapp have covered practically the 

 same ground. These men have placed their emphasis upon the 

 measurement of habitat factors in the study of plant and forest 

 distribution ; upon determining the factors which cause plant 

 succession ; upon the moisture requirements of plants of economic 

 value ; upon determining the wilting coefficients of plants in 

 various soils ; upon methods and means of determining more 

 satisfactory ways of classifying vegetation on the basis of climatic 

 factors ; and upon a variety of other phases of comparatively 

 lesser importance. 



As has been said before, modern plant ecology is dynamic. 

 More recently it has shown a tendency to become applied in 

 character (witness Shantz's work). While plant ecology started 

 as a study of plant distribution, it was not until about 1895 that 

 the emphasis shifted from the effect to the cause of plant distri- 

 bution. This led to the study of habitat factors. These were 

 found to show their influence mainly in the behavior of the plant, 

 hence plant ecology allied itself more closely with plant physiology. 

 The present physiological trend of work in plant ecology shows 

 two important phases (92). The one deals with correlating 

 physical factors with the distribution of plant and plant com- 

 munities ; the other deals with the correlation of physical factors 

 and physiological functions or processes. There is an ever in- 

 creasing number of works, especially on distributional problems. 

 Among those in this field in our own country we find Shantz in 

 the Great Plains, Fuller in the Chicago region, Pool on the Ne- 

 braska prairies, Transeau at Cold Spring Harbor, N. Y., Weaver 

 in Washington, Clements in the Rocky Mountains, and Shreve in 

 Southern Arizona (93). Among some of the workers on the 

 comparative physiology of associated plants we find Cannon upon 

 the optimum growth temperature of roots, Livingston and Shreve 

 upon the transpiring power of plants, Harris on the osmotic 

 strength of the saps of plants, and Richards and MacDougal on 

 several physiological aspects of the cacti. In this category is 

 also included the author's recent work upon the effect of habitat 

 factors upon the germination of forest tree seeds (94). 



Some of these investigations deserve further mention. The 

 recent work of Briggs and Shantz upon the wilting coefficient of 



