624 General and Applied Biology 



Each living plant has inherent tendencies to respond to certain stimuli 

 in certain specific ways. For instance, a certain species of plant responds 

 in a definite way to moisture, light, x-rays, cosmic rays, temperature, 

 gravity, etc. These inherent abilities to react in a definite manner in no 

 small measure determine how and where this species will be distributed 

 and the characteristics which such species will possess. 



3. Mutations and New Types of Organism. — Plants and animals which 

 have been accustomed to a certain habitat may mutate rather abruptly 

 and spontaneously. Such resulting mutants may be of such a variety 

 that they will require an entirely different environment from that of 

 their parents, so that the former will have to develop in the new habitats 

 or be exterminated. 



Natural crossing of plants, or animals, may result in offspring which 

 are so different from their parents that the offspring may have to de- 

 velop in a different kind of environment. In this case, as in the one 

 mentioned above, an entirely new ecologic relationship may be instituted 

 and consequently the distribution will be affected. 



4. The Inheritance of Specific Structures by Organisms Being Studied. 



— Such inherited structures as the gills of a fish or a crayfish naturally 

 limit their distribution to water, while the lungs of men, birds, rabbits, 

 and turtles necessitate their living on land. The sucking type of mouth 

 part of certain insects makes it necessary that they suck their nourish- 

 ment from certain hosts, while the chewing type of mouth part of other 

 insects determines their distribution on hosts of other types. Snails, in 

 order to build their characteristic calcareous shells, cannot live in acid 

 waters in which there is no lime. Certain insects, such as the common 

 "walking stick" (order Orthoptera), because of their resemblance to a 

 twig, are usually found in bushes where they are protected by their in- 

 herited morphology. These same insects distributed artificially on 

 smooth surfaces are easily exposed and thus exterminated. Many moths 

 and butterflies, because of their inherited structures and colorations, are 

 found in certain environments because they are afforded protection 

 there which they would not enjoy if they were distributed in an entirely 

 diff"erent environment. Certain animals inherit definite color patterns 

 by means of which they are partially hidden and protected by one type 

 of environment. If moved to another type of environment, these same 

 animals are easily detected and exterminated. These, as well as many 

 other illustrations, show the importance of inherited structures which 

 influence the ecologic relationships of the animals possessing them. 



