Influence of Environment j\^ 



boriously before him? Even the strongest defenders of the 

 inheritance of acquired characters are constrained to admit that 

 it occurs only sporadically and exceptionally. 



Neo-Lamarckism. — Many modifications of the Lamarckian hy- 

 pothesis of the inheritance of acquired characters have been pro- 

 posed in recent years. Foremost among these are the "mneme" 

 theory of Semon and the "centro-epigenesis" theory of Rignano. 

 To Semon as to many other biologists the apparent resemblance 

 between memory and heredity has seemed significant, and tluN 

 furnishes the basis of his theory. Semon holds that every condi- 

 tion of life, every functional activity of an organism leaves a 

 permanent record of itself in what he calls an "engramme.'' If 

 these conditions or activities are long continued their engrammes 

 are heaped up and affect heredity. Semon does not ask if "ac- 

 quired characters" are inherited, but rather "Are the hereditary 

 potencies of the germ cells altered by stimuli acting on the paren- 

 tal body?" This is a very different thing from the inheritance of 

 a particular acquired character, and there is some evidence that 

 such stimuli may in rare instances produce changes in the heredi- 

 tary constitution of the germ plasm though these evidences are 

 by no means conclusive. 



Temporary Effects of Environment; "Induction." — On the 

 other hand certain changes may be produced in germ cells or 

 embryos which last for only a generation or two and then dis- 

 appear. It is well known that plants grown in poor soil are 

 smaller and produce smaller seeds than those grown in good soil, 

 and deVries, Bauer and Harris find that such seeds produce 

 smaller plants having smaller seeds than do seeds of normal size. 

 This is an after effect of poor nutrition which changes the amount 

 of food material in the seeds and through this the size of the plant 

 which develops from the seed, but it does not change the heredi- 

 tary constitution. Woltereck found that in Daphnia there is an 

 after effect of cold lasting for one or two generations, and this 

 he calls "induction" when the effect lasts for one generation, or 

 "pre-induction" when it lasts for two or three generations. Whit- 



