THE SURVIVAL OF THE FITTEST 391 



the scales to give them their color, and withdrawn 

 during periods of rest or sleep. This accounts for 

 the slight change in the wing colors of the species 

 I have mentioned when they wish to mimic the 

 object on which they alight, and the regaining of 

 their normal color when they fly. 



There is, no doubt, a weeding-out process going 

 on, caused by the severe frosts which occasionally 

 visit the more tropical parts of Florida. The 

 tenderer trees and herbaceous plants are some- 

 times either killed outright or so weakened that, 

 for a time, the hardier ones gain a decided ascend- 

 ency. Then a series of mild winters gives the 

 tropical species their opportunity to forge ahead 

 and drive their rivals out, or at least to gain a 

 marked advantage. Several species of plants in a 

 wild state are particularly subject to the attacks of 

 certain insects which may seriously handicap them 

 in the struggle for supremacy or even existence. 

 In this region the wild fiddlewood (Citharexylum) 

 is almost constantly attacked by a tent caterpillar 

 which may destroy all the leaves on an entire tree. 

 A small beetle, apparently a Curculio, has for 

 some years pierced the seeds of our native Ocotea, 

 so that I have not been able to find a single perfect 



