Ecologic Study of Living Organisms 625 



Certain plant seeds through inheritance are suppHed with definite struc- 

 tures, by means of which they are disseminated. Claws, hooks, spirals, 

 etc., may help such structures in being transported by animals, insects, 

 birds, and the wind. The inheritance of certain structures for purposes 

 of controlling the process of transpiration naturally will determine the 

 distribution of such plants in various environments. The method of car- 

 ing for transpiration on the part of cactus plants is such that they are 

 able to exist in arid habitats, while plants which have not inherited such 

 mechanisms cannot exist under such conditions. Hence, the distribu- 

 tion of these opposite types is somewhat predetermined. 



The root systems of certain plants are such that they cannot possibly 

 supply the necessary materials and provide the necessary anchorage and 

 support in certain types of soils. In other words, certain types of roots 

 make it necessary that such a plant be distributed in soils for which such 

 roots are fitted. 



Certain combinations of genes in plants sometimes result in a lack 

 of development of chlorophyll. Naturally, such plants cannot long exist 

 and the result is that the distribution is affected. 



5. The Rates of Metabolism of the Organism Being Studied Ecolog- 

 ically. — Animals usually inherit certain rather definite, normal rates of 

 metabolism. Certain factors of the environment are conducive to this 

 normal rate, while other factors are not. To be successful, the animal 

 must find that environment in which its particular rate of metabolism 

 may be developed properly. If it cannot find such an environment, or 

 because of an inherited lack of ability cannot locomote to better regions, 

 it may die because of an abnormally induced rate of metabolism. This 

 may prove to be a large factor in the ecologic relationship of that animal. 



B. Environment 



1. Physical Factors. — 



(a) Temperature: Most animals have an optimum temperature at 

 which their metabolic processes react best and at which they live most 

 successfully. They also have a minimum and a maximum below and 

 above which they will not live. Hence, animals will tend to select, as 

 far as possible, those temperatures in which they can best exist. Freez- 

 ing of water in which animals live affects them in the following ways: 

 (1) some become hard and inactive during the frozen period; (2) oth- 

 ers escape the freezing by burrowing deep in the mud; (3) others die 

 under such conditions, but only after they have made the necessary 



