OUR DEPENDENCE ON FORESTS. 15 



of a mixture of the gases oxygen and nitrogen. The 

 former is that on which all animals, including man, and 

 indeed all living organisms, are dependent for breathing; 

 so far as that function is concerned, the latter is useful 

 only as a diluent. Of the other components in the 

 atmosphere, one of the chief is carbonic acid gas (C0 2 ). 

 This gas is. produced mainly by combustion and by the 

 breathing of all living organisms. By both of these 

 processes a large amount of oxygen is used, is combined 

 with carbon, and returned to the atmosphere as CO 2 . If 

 this process went on without another of a counteracting 

 nature, the inevitable result would be that atmospheric 

 oxygen would gradually diminish, with a corresponding 

 increase of CO L >, which ultimately would produce a 

 condition in which life would be impossible. Indeed, some 

 scientists have asserted that with our present extravagant 

 method of the use of nature's products, we are actually 

 hastening on to such a state. Others declare that science 

 will intervene by inventing some means of liberating 

 oxygen from oxides abundant in the earth, and thus 

 maintain a sufficient supply for all purposes. But nature 

 has a use for C0 2 in the atmosphere, and also a means of 

 removing it, and if a proper balance can be maintained by 

 natural means there will be no occasion for science to make 

 up the deficiency of oxygen by artificial means. All green 

 plants in the presence of sunlight use up CO 2 from the 

 atmosphere. The green leaves of plants take in this gas, 

 utilise the carbon, and return to the air part of the oxygen. 

 Of all plants, trees provide the greatest leaf-surface on a 

 given area of the earth. It follows that if a balance is to 

 be maintained in the atmosphere, a proper proportion 

 of every country should be devoted to forests. Further, 

 trees can be successfully raised on land which will not 

 produce other useful crops ; and if such land is devoid of 

 plants, excepting a scanty covering- of heaths, useless 

 grasses, and mosses with the most meagre leaf -surf ace, 



