Ecological Points 21 



Water, available in such a way that it can be absorbed 

 by the roots; this depending upon physical and chemical 

 conditions of the soil. 



Minerals, of certain kinds, in available form but only in 

 small quantities, such as are found in almost all soils. 



Air, for respiration. 



The amount required of these supplies varies with differ- 

 ent species and with their gradual adaptation to existing 

 conditions, also with the conditions at the other end, namely, 

 the environment of the foliage. 



Here the indispensable air for respiration and carbon 

 supply is almost invariably present, but in addition there 

 are required: — 



Certain conditions of the air as regards temperature and 

 humidity in order to produce the so-called transpiration, 

 i.e., evaporation of water from the leaf surface. This pro- 

 duces a stream of water flowing from the roots through the 

 young wood, the carrier of minerals upward and of assim- 

 ilated food materials downward as needed. 



In addition there is necessary: 



Light of certain intensity to produce the chemical action 

 in the leaves by which the food materials are digested or 

 assimilated. 



Ecological Points. This relation and adaptation of the 

 plant to its surroundings has been called its ecology. 



Some of these conditions of environment are unalterable 

 in any locality and situation; cHmate in general and the 

 seasons being, of course, uncontrollable by man. 



The adaptation of species to given cHmates has been 

 accomplished during ages in such a manner as to assign 

 to them fields of distribution within which they are found 

 by nature, i.e., within which they can perform their life 

 functions satisfactorily. This process of adaptation is 



