547 



Croonian Lecture. — Alterations in the Develo^yment and Forms 

 of Plants as a Result of Enviro7iment.* 

 By Prof. G. Klebs, University of Heidelberg. 



(Lecture delivered May 26,— MS. received June 2.5, 1910.) 



I have to-day the great honour of delivering an address before the Eoyal 

 Society, so long renowned as a centre of natural science ; but I do so with 

 a certain hesitation, being aware that I am not sufficiently master of the 

 English language, and have had but little time for preparation. In 

 consideration of this, I shall avoid entering too much into theoretical 

 discussion ; I wish rather to lay stress upon the demonstration of the results- 

 of my experiments upon the Influence of Environment on Plants. 



The problem of the relations of the organism to its surroundings is very 

 old, but it has only recently become an object of active research. In all 

 branches of biology, as well as in the different fields of history, educational 

 science, and so forth, we meet this fundamental problem and also the most 

 conflicting views on it, some of which suffer from exaggeration of the influence, 

 of environment, othei'S from its under-estimation. 



We naturalists are guided above all by experience, and we use theoretica 

 opinions to select such questions as can be tested by experiments. In this- 

 way physiology tries to recognise the life-processes in their dependence 

 on external factors. Nutrition, growth, and all phenomena associated with 

 stimulus and movement have been studied with great success. On the other 

 hand, the phenomena connected with the production of forms have been: 

 neglected, remaining exclusively a branch of the purely descriptive science of 

 morphology. In modern times, however, physiology claims to penetrate 

 this mysterious region by means of experiment. 



One of the most striking features of an organism is its development from 

 a fertilised egg to maturity. Every species goes through a clearly defined 

 development, and shows from its first genesis a complicated series of successive 

 changes of form, of which each is the necessary outcome of its predecessor. 

 This exceedingly regular course of development, consisting of successive 

 internal alterations, is preserved under different conditions of life. 



We can understand the presumption, considered self-evident in former 

 times, and having its supporters even now, that this development is the 

 expression of the inscrutable inner nature of plants. According to this, 



*■ The Lecture as delivered was* illustrated by numerous photographic slides, the 

 publication of which is deferred for the present. 



VOL. LXXXII. — B. 2 T 



