TRANSMISSION OF ACQUIRED CHARACTERS. 405 



of the observer (for the observations have already been made) so 

 much as that of the thinker. It is not a correct train of reasoning- 

 to conclude that after-effect and heredity are identical in nature, 

 from the fact that certain periodical influences, acting upon a single 

 individual, set up periodical physiological processes which continue 

 for a time after the influences have ceased to act. We might 

 almost as well argue that the oscillations of a pendulum, which, 

 continue as after-effects when the pendulum has been set going, 

 are of an identical nature with the process of heredity. All these 

 phenomena have indeed this much in common : a cause which 

 acted at some time in the past, but which is no longer visible at 

 the time when the phenomenon appears. But the likeness ends 

 here, and the supposed identity in nature merely depends upon wild 

 speculation. One difference is very obvious, for the phenomena of 

 after-effect gradually cease after the withdrawal of the stimulus, 

 just like the oscillations of the pendulum, while the pheno- 

 mena of heredity continue without any interruption. As far as 

 heredity is concerned the physiological processes of after-effect are 

 not distinguishable from any of the other well-known acquired cha- 

 racters which are recognizable as morphological changes. After- 

 effects are not transmitted, and compared with this fact but little 

 importance can be attached to the use of vague analogies by Detmer, 

 who would wish to conclude that heredity is only the after-effect 

 of processes which had been set going in the parent organism. 



At the end of his paper Detmer applies the ideas which he has 

 gained from the consideration of after-effect to certain phenomena 

 in the normal life of plants. He suggests that the periodical 

 change of leaf in trees and shrubs may have been produced by the 

 direct effect of climate. If branches bearing winter buds are cut 

 off in the autumn and are placed in a hot-house, with their cut 

 ends in water, the buds do not at once develope, and months may 

 often elapse before they begin to break. He argues that this 

 experiment proves that the annual periodicity of the plant no 

 longer depends directly upon external influences ; these latter pro- 

 duced the periodicity at some earlier time, but it has been gradually 

 fixed in the organism by after-effect and heredity (!), so that its 

 disappearance does not now take place when the stimulus is with- 

 drawn, and changes would only happen very gradually under the 

 influence of changed climatic conditions. He considers that this is 



