90 Heredity. 



If this experiment is impossible, if all the tmnsplant- 

 ed trees die, and if the seeds fail to germinate in fertile 

 gronnd, there will be no way to show whether tlie pecu- 

 liar characteristics of the species are or are not heredi- 

 tary. 



We know that organisms may be modified in many 

 ways by the direct action of external conditions, but a 

 few illustrations wnll not be out of place. 



Hemp-seed causes bullfinches and certain other birds 

 to become black, and w^e know from the observations of 

 many naturalists that caterpillars which are fed on dif- 

 ferent kinds of food either themselves acquire a different 

 color, or they may produce moths which differ in color. 

 Many curious cases of this kind have been noticed in 

 birds and insects, and if unnatural food causes devia- 

 tions from the natural color of a species, it is quite pos- 

 sible that the normal color may in many cases be due di- 

 rectly to the action of the normal or natural food. 



Darwin gives many instances of plants which are 

 characterized by a certain peculiarity in one country, 

 while in another country this peculiarity is almost or en- 

 tirely lacking. Thus when the American sassafras tree 

 is grown in Europe, it loses its aromatic flavor. In India 

 the fibres of flax and hemp are brittle and useless, and 

 the latter plant yields a resinous narcotic substance, 

 hasheesh, which is used as an intoxicating drug, but in 

 England this property is lost and the fibre becomes long 

 and tough. Large, finely-flavored, and brightly-colored 

 American apples, when reared in England, jiroduce fruit 

 of a dull color and poor quality. 



In these cases w^e are unable to state what the deter- 

 mining conditions are, but the fact that peculiarities 

 are made to disappear by a change from one country to 

 another shows that they are not congenital but are due 



