702 THE RELATION OF INSTITUTIONS TO ENVIRONMENT. 



adaptive devices for checking evaporation and storing water, for pro- 

 tecting the plants from heat and cold, and for arming them against 

 animal enemies, as well as for utilizing the energy of light, are developed ; 

 here all plants interact with the inorganic external in such manner 

 that even unrelated species assume likeness in form and feature. In 

 desert lands the strife for existence is not between plant and plant, 

 whether akin or alien, so much as against sun and sand; and most of 

 the organisms engaged in this common strife are forced thereby into a 

 cooperation in which each benefits the other and in which finally all are 

 united in a great solidarity of singular perfection. So the organisms of 

 desert lands, especially the plants, are modified by environment in the 

 direction of likeness in external characters, and in other ways, and are 

 forced into a cooperative union transcending specific and even generic 

 kinship; and thereby the flora is in large measure transformed, and the 

 potency of heredity is masked through the adjustment of the organisms 

 to environment, while vegetal clanship is exalted into plant sociology. 

 In humid and in arid lands alike heredity and environmental inter- 

 action are commonly antagonistic, and in this antagonism the strife for 

 existence arises; but now and then, in the course of the development 

 of organic forms, it chances that an organism enters an environment 

 to which it is so peculiarly adapted that the struggle for existence is 

 made easy through the conjunction of heredity with external relation, 

 and in such instances the potency of vitality is strikingly shown. Such 

 a case was that of the American buffalo which, about the time of transi- 

 tion of geologic modernity into historic antiquity, began to spread over 

 the grass-covered plains of the mid-continent; so well adapted was his 

 environment to his needs that his kind increased and multiplied a 

 hundred fold; his rise was so rapid that he far outstripped enemies 

 and expended his redundant energy in covering the hills and valleys 

 with thousand- weights of moving flesh; but through generations of 

 peace and sloth his vigor waned, his constitution weakened, and he fell 

 an easy prey to the red man, and when the white man came he melted 

 away helplessly. Commonly such spurts of vitality as that exemplified 

 in the history of the buffalo result from human interference with the 

 natural interaction of organisms. The European rabbit, when intro- 

 duced in Australia, escaped the enemies and inimical factors of envi- 

 ronment which had grown up with the species in the original habitat, 

 and soon increased beyond anticipation, almost beyond belief; the 

 western American rabbit found his environment changed by the intro. 

 duction of fields and stock, and increased enormously; the English 

 sparrow, the common daisy of Britain, a roadside plant of Mexico, and 

 many other organisms introduced in the United States artificially have 

 profited by freedom from natural enemies and have multiplied into pests. 

 So, in many parts of the world, and at various times in the history of 

 the development of organisms, the redundance of vitality, when relieved 

 from the pressure of adverse conditions, has been exemplified; and it 



