ECOLOG y. 301 



563. In carrying on studies of this kind one should bear in 

 mind the factors which influence plants in these relationships, 

 that is, \vhat are called the ecologic factors ; in other words, 

 those agencies which make up the environmental conditions of 

 plants, all of which play a greater or lesser role in the habit or 

 status of the plant concerned, and which, acting on all plants 

 concerned, gi\e the peculiar color or physiognomy to the plants 

 of a region or of a more restricted community. 



Such factors are climate, with its modifying meteorological 

 conditions ; texture, chemistry, moisture content, covering, to- 

 pography, exposure, etc., of the soil; influence of light and 

 heat ; of animals, of plants themsehes, and so on. 



