ACQUIRED CHARACTERS 41 



under which the insect passes its chrysahs stage ; also 

 mice which are reared under warm conditions are found 

 to have shghtly longer ears and Umbs than those reared 

 in colder temperatiures. 



It \nR be evident that it may sometimes be difficult 

 to say whether such results are really modifications, or 

 are due to variations induced in the germ plasm. 

 Where we can see the body adapting itself to new con- 

 ditions we may confidently class the changes as true 

 modifications. But where we observe simply a change, 

 without being able to trace its purpose, we have still to 

 discover whether it began in the body or in the germ 

 cells. This, therefore, introduces a comphcation. 



With regard to the inlieritance of such modifications 

 it must be said that the great burden of results is again 

 negative. Alj)ine plants when brought do^^'n to low 

 altitudes become taUer, broader leaved, and, in short, 

 lose much of their alpine character. This change seems 

 to be complete in the first generation, and persists as 

 long as the plants remain imder lowland conditions. 

 But on returning the plants to their original habitat, 

 the original alpine habit also retmTis, and remains 

 constant through generations. 



Yet in this connection we have one rather interest- 

 ing case which seems to show just the opposite. In 

 Turkestan there exists a plant nearly allied to our 

 ordinary " shepherd's purse " : from its distribution it 

 appears certain that it has been accidentally spread 

 from the low country to higher altitudes along the fine 

 of a very old trade route. The form existing on the 

 higher ground is smaller than that found in the original 

 habitat, and there are other differences. Moreover, 

 the highland form is pink-flowered, whereas the other 

 is white. Now, when the lowland form is transferred 

 to higher districts it becomes exactly like the native 

 variety, even to the pink flower. Changed back, it 

 assumes its original form. But when the higliland 

 form is brought down to the home of Its ancestors it 

 retains its character, pink flower and all. Wliat could 

 be more obvious than that the change produced by 



