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, 
2.€., 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, climate in general and the 
seasons being, of course, uncontrollable by man 
The adaptation of species to given climates has been 
accomplished during ages in such a manner as to assign 
to them fields of distribution within which they are found 
by nature, z.e., within which they can perform their life 
functions satisfactorily. This process of adaptation is 
