Development of Natural History. 141 



(1814), of high value, and also by Behlen, Gwinner and 

 Hartig. 



In the direction of plant physiology, Cotta, early and 

 creditably, attempted (1806) to explain the move- 

 ment and function of sap, but remained unnoticed. 

 Mayer's (1805-1808) essay on the influence of the 

 natural forces on the growth and nutrition of trees, 

 contains interesting physiological explanations for 

 advanced silvicultural practice. But these sporadic 

 attempts to secure a biological basis were soon for- 

 gotten. Not until Theodor Hartig (1848) published 

 his Anatomy and Physiology of Woody Plants was 

 the necessity for exact investigation of forest biology 

 as a basis for silvicultural practice fully recognized. 

 With the development of general biological botany 

 or ecology, a new era for silviculture seems to have 

 arrived,. Perhaps in this connection there should 

 be mentioned as one of the earlier important contri- 

 butions of much moment, G. Heyer s Verhalten der 

 Bdume gegen Licht und Schatten (1856) in which the 

 theory of influence of light and shade on forest de- 

 velopment was elaborated. 



Among those who placed the study of pathology of 

 forest trees on a scientific basis should be mentioned 

 first Willkomm (1876), followed by R. Hartig. 



In zoology, the early writers began with a descrip- 

 tion of the biology of game animals. Next, interest 

 in forest insects became natural, and, in -1818, Bech- 

 stein in his Encyclopaedia devoted one volume (by 

 Scharfenberg) to the natural history of obnoxious 

 forest insects. Toward the middle of the century, 

 with the planting of large areas with single species, 



