CHAP, c ORIGIN OF SPECIES 373 



Direct adaptation or self-regulation appears to find its field of operation 

 largely in vegetative organs and in the sphere of metabolism. The 

 flowering shoot in its development follows laws that, in some ways, differ 

 entirely from those concerning vegetative organs ; at least, so far as is 

 known, its reactions to climate and soil are far slighter. This is essentially 

 due to the facts that the flowering shoot is short-lived and that metabolic 

 processes play a less important part than in connexion with vegetative 

 shoots. 



It seems to be beyond doubt that characters peculiar to growth-forms 

 have arisen through direct adaptation to the environment or natural 

 self-regulation operating through countless generations, and that at the 

 same time the acquired characters have been fixed to a greater or less 

 extent by heredity' (which is antagonistic to new adaptations). In this 

 matter Lamarck had a keener eye for the truth than many modern 

 investigators appear to possess. Nevertheless this suggested course of 

 evolution must be regarded as a hypothesis, as the inheritance of ' acquired 

 characters ' has not been completeh' proved. Yet when one keeps in 

 mind not only the facts and experiments here recounted, but also ephar- 

 monic convergence, vicarious species or forms at different altitudes or in 

 different soils, physiological races, and additional facts supplied by Von 

 Wettstein ^ and others, then our doubts seem resolved. From day to 

 day new experiments go to prove that the direct action of external factors 

 can modify the plant's nature and can evoke hereditary distinctions in 

 form : an admirable example of this is provided by MacDougal's ^ recent 

 experiments on the effect of injecting chemical bodies into the ovary. 

 Direct adaptation is beyond doubt one of the most potent evolutionary 

 factors in the organic world, and appears to play the leading role in tlie 

 adaptation of growth-forms and formations. And its study will dispel 

 some of the darkness shrouding the mystery of life, though we cannot 

 hope to reach the heart of that mystery.^ 



' Von Wettstein, 1898. ' .AlacDougal, 1906 a, p. 129. 



^ Special literature: Lamarck, 1809; Darwdn, 1859; Gobel, 1907 ; Klebs, 1905 ; 

 Von Wettstein, loc. cit. ; Diels, 1906; Warming, 19086. 



