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ECOLOGY 621 
tropophytes. ‘The deciduous forests, which include the oaks, 
the beeches, the ashes, the maples, the walnuts, the chestnuts, 
cover a part of eastern and western China, central Europe 
(England, France, Belgium, Germany) and eastern Australia, 
and are coincident with the countries occupied by the most 
civilized races of man, such as the Americans, Europeans, 
Chinese and Japanese. ‘The cold temperate climatic conditions 
which have determined the distribution of the forest trees have 
been influential also in the development of the energetic races of 
mankind. 
PLANT SuccEssion.—In the development of vegetation, the 
same region becomes successively occupied by different com- 
munities of plants. This process is called plant succession. 
There are two kinds of plant succession, (1) the Aydrarch which 
begins in water and (2) the xerarch which may begin on bare 
rock, rocky talus slopes, or other location where the soil is 
extremely dry. As the scope of this book forbids little more than 
mention of this topic, the student interested in it is referred to 
works on plant ecology. 
RELATION OF PLANTs TO ANIMALS 
The great and fundamental réle of green plants in the world’s 
economy is that of constructing highly complex organic com- 
pounds for food out of simple, inorganic, raw materials. This 
food, part and parcel of their very bodies, is eaten by animals 
whose chief and contrasting réle is that of breaking down the 
plant food into its simplest elements. 
The raw materials which constitute the ordinary diet of 
green plants represent salts of various metals, such as nitrates, 
phosphates, sulfates, etc., the water which they absorb from the 
soil, and carbon dioxide which they inhale from the air during 
sunlight. 
Carnivorous PLANTS.—There exist, however, about 500 
species of green plants which, in addition to the common habits 
of nutrition possessed by their relatives in the vegetable world, 
have acquired the luxurious appetite for the flesh and blood of 
animals. These exhibit a variety of devices for the allurement, 
capture, imprisonment, digestion and absorption of their prey. 
