A New Theory of Heredity. ' 91 



to something outside the plant, which is present in 

 one country but absent in another. The following in- 

 stance, which is given by Darwin, is most interesting 

 '•'Mr. Salter, who is well known for his success in culti- 

 vating variegated plants, informs me that rows of straw 

 berries were planted in his garden in 1859, in the usual 

 way; and at various distances in one row several plants 

 simultaneously became variegated, and what made the 

 case more extraordinary, all were variegated in precisely 

 the same manner. These plants were removed, but dur- 

 ing the three succeeding years other plants in the same 

 row became variegated, and in no instance were the 

 plants in any adjoining row affected." He also says that 

 in certain parts of India the turkey becomes reduced in 

 size with the pendulous appendages over the head enor- 

 mously developed. 



In these cases it is difficult to determine what has 

 caused the change, but in other instances this is more 

 obvious. Thus Darwin states that good authorities as- 

 sert that horses ke^^t during several years in the deep 

 coal mines of Belgium become covered with velvety 

 hair almost like that of the mole, and he quotes from 

 Dr. Falconer the statement that the Thibet mastiff and 

 goat when brought down from the Himalayas to Kash- 

 mir lose their fine wool. 



These are only a few of the cases which Darwin gives, 

 and many more might be added from other authorities, 

 but I have given enough to show that external condi- 

 tions of life may act in one country to cause certain 

 modifications which are entirely absent in another coun- 



try- 



The change of Artemia into Branchippus, by rearing it 

 in fresh water, is one of the most remarkable instances 

 of definite modification due to a change of external 



