41 8 ON SUPPOSED BOTANICAL PROOFS OF [VII. 



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 phenomena 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 characters which are recognizable as morpho- 

 logical changes. After-effects are not transmitted, and com- 

 pared 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 b}^ 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 produced 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 take place when the stimulus is withdrawn, and changes would 

 on^.y happen very gradually under the influence of changed 

 climatic conditions. He considers that this is proved from the 

 fact that our cherry has become an evergreen in Ceylon. 



Such are Detmer's opinions, and every one will agree with 

 him in believing that the periodical change of leaf in temperate 

 climates has been produced in relation to the recurring alter- 

 nation of summer and winter. This is certainly the case, and 



