114 PLANT PHYSIOLOGY 



plant physiology, and is to be seen in the development of our science 

 clearly enough. One needs only to compare the older works of Sachs 

 with his last book, Lectures on Plant Physiology. In the latter work 

 for the first time morphology comes into living relations with physi- 

 ology, and this is more clearly evidenced by his presentation of 

 anisotropy, in which he makes the attempt to explain the relation 

 between the formation and the direction of plant organs under the 

 influence of constant outside directive forces. Similar attempts to 

 explain the form-relations of plant organs from analogous points of 

 view were made soon after. Everywhere the most intimate rela- 

 tion between form and structure, and function, was sought after. 

 This research was directed not only at causal but also at teleologi- 

 cal explanations, for which experimental evidence was, as far as 

 possible, advanced. Schwendener and his school were active in both 

 directions, furthering the union of morphology and physiology, and 

 thus laying the foundations for a physiological plant anatomy. 



The increasing invigoration of physiology by morphology has in 

 more recent times been of the same importance for the further de- 

 velopment of our science as the influence of Darwin's basic idea of 

 phylogeny was to numerous problems concerning plant life. The 

 question which now stands to the front is, how have forms arisen, 

 and what functions are bound up with morphological relations, and 

 also how we are to distinguish between ontogenetic and phylogenetic. 

 E. g., Has a particular form or a particular tendency of an organ 

 originated with the individual, or is it referable to inherited pecu- 

 liarities, or is it the product of ontogenetic and at the same time 

 of phylogenetic development? 



The study of ontogeny is the peculiar domain of physiology in the 

 narrower sense that is, the mechanics, chemistry, and physics of 

 the living organism so far as the development which takes place 

 before our eyes is approachable by direct observation and experi- 

 ment. That which may be determined inductively concerning the 

 life, the origin and fate of plants and the plant world may be got at 

 only by following the individual development. 



The riddle of ontogeny, and the question of phylogeny (which 

 is well-nigh unanswerable by direct methods) open the door of specu- 

 lation, and the scope of the problems of the origin and development 

 of the organic kingdom are thus discovered. These have stimulated 

 many students outside of the circle of the observational and experi- 

 mental sciences to seek help, or at least suggestion, in philosophy. 



Indeed, at the present time the philosophical element in natural 

 science has come strongly to the front. The reawakening of research 

 in the theory of descent is indeed the chief cause of this modern phe- 

 nomenon, which, I believe, commenced in the organic natural sciences, 

 and then passed over into the inorganic. 



