LIXTiEAJf SOCIETY OF LONDOTf. 77 



This kind of variability, which we now call modification however, 

 does not count as it is not trausniittable. 



About the Inheritance of Acquired Characters 



I will say but little. In the face of Joliannsen's and Vilmorin's 

 experience with selection in pure species, such an inheritance is 

 very improbable. I should like to lay further stress on the fact 

 that Viliuorin cidtivates wheats from uiost varying parts of the 

 world, and that some of them have pro|jerties which are frequently 

 ascribed to the climate from which that particular variety came. 

 Tet all remain perfectly true to type in Verrieres. I have myself 

 long believed in some kind of inheritance of acquired characters, 

 in spite of the scanty evidence, because I saw no other way to 

 account for the origin of new forms or of what is usually called 

 A'^ariability. Now I think that I can account for this in another 

 way. I cannot myself offer any new facts to this vexed question, 

 and will therefore refer to two authorities with whom I fully 

 agree. On the botanical side Klebs, who has perhaps made more 

 careful experiuients bearing on this question than anybody else, 

 states in Bateson's ' Problems of Genetics ' in German what I 

 here render in English : — " But up to the present no certain case 

 is known in which the artificially produced character was trans- 

 mitted through several generations under the usual 'normal' 

 conditions." 



On the zoological side Bateson says : — " In reading such papers 

 as those of Semon or Kammerer, the thought uppermost: in my 

 mind is that to multiply illustrations of supposed transmission of 

 acijuired characters is of little use until some one example has 

 been thoroughly investigated." 



He then gives some examples of the kind of evidence he would 

 consider conclusive and continues : — " Till evidence of this kind is 

 published by at least two independent observers investigating 

 similar material, I find it easier to believe that mistakes of obser- 

 vation or of interpretation have been made than that any genuine 

 transmission of acquired characters has been witnessed." 



This is exactly my position, and I know of no case furnishing 

 definite proof of the inheritance of an acquired character. I know- 

 quite well that this is no way of treating the question, which is 

 yet supported by so many able biologists, and I had intended to 

 say more about it, but the time is too short. 

 Let us now consider 



Spontaneous Variation, 



or what is now more usually called mutation. Of this, two kinds 

 more particularly concern us — the so-called progressive mutation 

 caused by a factor being added to the stock of hereditary factors 

 already present, and mutation by loss of a factor. The third 

 and very doubtful kind of mutation caused by the change of a 

 factor into another can be passed by, as the evidence for it is 



