102 THE NATURE OF LIFE 



as close to the surface as possible. In 

 the lowland the same plants grow up- 

 right and have a very different aspect. 

 Experiment shows that by placing the 

 plants on ice every night in the lowland 

 they can be made to assume the curious 

 aspect of the alpine situation. 



Very striking effects are observed in 

 insects. By exposing butterflies in the 

 chrysalis stage to high or low temper- 

 atures we are able to change their colors 

 in a remarkable manner: the same species 

 treated in this manner may produce va- 

 rious forms which occur in nature and 

 were at one time regarded as different 

 species. 



Stockard has found that when devel- 

 oping trout are cooled at certain stages 

 of development all degrees of doubling 

 are observed. In some cases the fish has 

 two heads, in others two tails, or the body 

 may be double throughout. 



A doubling may also be produced by 

 simple physical means in the case of cer- 

 tain eggs. Loeb was able to produce 



