28 NATURE SKETCHES IN TEMPERATE AMERICA 



be due to geographical barriers, to migration, or to any other 

 state of matters leading to exclusive breeding within the 

 separated group." '■ 



Numerous examples of special adaptations are given through- 

 out this book. For instance, in the tree toad, which often 

 selects the bark of trees to rest upon, the color changes so as 

 to simulate exactly the colors of its surroundings, its body often 

 appearing like a rounded excrescence oir the bark. All the 

 grasshoppers, notably the katydids, such as shown in the 

 colored plate of the cone-head (facing page 22), are colored 

 in simulation of their surroundings. 



Then we have the walking-stick whose attenuate body 

 resembles the twig of a tree. The humming-bird's bill and 

 tongue are so modified as to gain ready access to flowers such 

 as the columbine. Again, the modifications of the biting mouth- 

 parts of grasshoppers and the suctorial tongue of the butter- 

 flies offer examples of adaptations familiar to all. It is readily 

 conceived that the front legs of the mole cricket and those of 

 the ordinary garden mole have been adapted and perfected to 

 a particular kind of environment, of tunnelling under the 

 ground. 



While the conditions under which organisms of a specialized 

 type remain the same, the species may be able to maintain 

 themselves, but it is readily seen that extermination would 

 likely follow any radical changes in the environment. 



Plant Adaptations 



In the dispersal of seeds of plants many contrivances have 

 become specialized to assist in carrying them to places favor- 

 able to their germination and growth. The winged seeds of 

 the maple and elm, the small, downy, and paraclmte-Hke 

 structure of the milkweed and wild lettuce, present broad 

 surfaces to the wind by which the seed is carried abroad. 

 Others are provided with hooks, such as the burdock, and 

 often become attached to the fur of animals. Again, there 

 are many hard seeds that are contained in eatable fruits 

 which are devoured by birds and mammals, and pass through 



• Post-Darwinian questions in "Darwin and After Darwin," Part III, p. 2. 



