EVOLUTION OF THE COLORS OF BIRDS. 37 



morning. Now the cause of this daily periodicity in the 

 flow of sap depends upon the periodical changes due to 

 the light to which the plant was exposed when it was 

 growing under normal conditions. When plants which 

 have been grown in darkness from the first are similarly 

 treated, the flow of sap does not exhibit any such peri- 

 odicity." In commenting on these instances, Weis- 

 manii says: "All this is certainly very interesting, and 

 it proves that periodical stimuli produce periodical pro- 

 cesses in the plant, which are not immediately arrested 

 when the stimulus is withdrawn, and only become uniform 

 gradually and after the lapse of a considerable time. But 

 I certainly claim the right to ask what connection there is 

 between these facts and the transmission of acquired 

 characters? All these peculiarities produced by exter- 

 nal influences remain restricted to the individual in 

 which they arose; most of them disappear comparatively 

 soon, and long before the death of the individual." 



From the theoretical standpoint of Prof. Weismaiin 

 this is doubtless correct. But it has been shown, I think, 

 that Prof. Weismann's theory of the continuity of germ- 

 plasm is not only unproven but highly improbable. 

 Moreover, it has been shown that the continuity of the 

 body plasm is highly probable. But if this be true, 

 then there is, to say the least, a strong analogy between a 

 rhythm which can be established in the somatoplasm 

 and repeated during the life of the individual and a 

 rhythm which can be established in the history of a 

 race. 



Cunningham has well pointed out, however, that the 

 Neo-Lamarckians do not claim that a change due to the 

 environment can be established in a single generation. 

 All that is claimed is, that when a particular environ- 

 mental influence is continued from generation to gen- 

 eration, the offspring successively inherit a progressive 



