In the direction of plant physiology, _Cotta_, early and creditably, attempted (1806) to explain the movement 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 forgotten. 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 contributions of much moment, _G. Heyer’s_ _Verhalten der Bäume gegen Licht und Schatten_ (1856) in which the theory of influence of light and shade on forest development 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 _zoölogy_, the early writers began with a description of the biology of game animals. Next, interest in forest insects became natural, and, in 1818, _Bechstein_ in his Encyclopædia 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, insect pests increased, hence the interest in the life histories of the pests grew and gave rise to the celebrated work by _Ratzeburg_, “_Die Waldbverderber und Ihre Feinde_” (1841). A number of similar hand-books on insects and on other zoölogical subjects followed; the latest, a most complete work on insects, being still based on Ratzeburg’s work, is that of _Judeich and Nitzsche_, in two volumes (1895). Of course, the general works on forest protection always included chapters on forest entomology. The first of these text-books on forest protection was published by _Laurop_ (1811), and others by _Bechstein_, _Pfeil_, _Kauschinger_ and recently by _Hess_ (1896), and _Fürst_ (1889). * * * * * _Knowledge of the soil_ was but poorly developed in the encyclopædic works of the earlier part of the period. Not till Liebig’s epochmaking investigations was a scientific basis secured for the subject. Then became possible the improvements in the contents of such works as _Grebe_ (1886), _Senft_ (1888), and of _Gustav Heyer_, whose volume (_Lehrbuch der Forstlichen Bodenkunde und Klimatologie_, 1856), well records the state of knowledge at that time. But only since then has this field been worked with more scientific thoroughness by _Ebermayer_, _Schrœder_, _Weber_, _Wollny_, and by _Ramann_, whose volume on _Bodenkunde_ (1893) may be still considered the standard of the present day (newest edition, 1910).