3. Mistaking the reappearance of a- modification for the 

 transmission of a modification. — For example: Nageli 

 brought Alpine hawkweeds to Munich, and as a result of 

 the new conditions they assumed new habits, which their 

 descendants also possessed. These modifications were im- 

 pressed upon each generation by the new conditions, but 

 when these plants were returned to their Alpine habitat 

 they assumed their Alpine characters. 



4. In the case of microbic diseases, mistaking reinfeci- 

 tion for transmission. Simply because a parent diseased 

 with tuberculosis or syphilis may have offspring affected 

 with the same disease does not make these diseases herit- 

 able. The children most probably become affected before 

 birth during the gestation period. 



5. Changes in the germ cells along with changes in the body 

 are not relevant. That alcoholism runs in families may be 

 perfectly true; the probable explanation is that germ cells, 

 as well as body cells, are poisoned, and the offspring may 

 show similar peculiarities as the parent. It may be, how- 

 ever, that a deficiency of control of alcohol is inherited. 



6. Failure to distinguish between inheritance of a particu- 

 lar modification and that of indirect results, or of correlated 

 changes of that modification. The blacksmith, for example, 

 acquires a strong right arm through use, and his occupa- 

 tion is one that contributes to the healthy nutrition of every 

 organ of the body. It is quite possible that the children of 

 blacksmiths have stronger right arms than the children of 

 parents engaged in sedentary occupations — on account of 

 the indirect or secondary effect of the better nutrition of the 

 whole body, including the germ cells. 



The old Hebrew proverb: "the fathers have eaten sour 

 grapes and the children's teeth are set on edge" (Ezekiel), 

 represents the belief in inheritance of modifications. As 

 Thomson remarks, one would have to enquire carefully, 

 however, whether the children had not been in the vine- 

 yard too, before coming to a conclusion that the acquired 

 character in this case had not been transmitted. 



7. Appealing to data from fewer than three generations. 

 This is quite a common mistake in discussions of this nature. 

 Modifications may occur for one or two generations, but 

 disappear in later generations. 



8. Transmission in unicellular organisms is not to the 

 point. As they have no "body" distinct from the germ 

 plasm, the term acquired characters does not apply (Thom- 

 son, Heredity). 



60 



