THE EARTH FOR MANKIND 545 



much of our soil to be wasted (see section 74). Making better 

 use of what we have includes the reclamation of lands through 

 drainage and irrigation (see Chapter VIII), and the elimination 

 of weeds, plant and animal diseases, and other enemies. 



In this country we have become aware of the need of a 

 national conservation policy only within a comparatively short 

 time. Until about the end of the nineteenth century most people 

 thought nothing of the rapid destruction of our forests, the 

 rapid exhaustion of our coal mines and other mineral resources, 

 and the rapid ruining of many streams as sources of fish. All 

 these results were accepted as part of the business of "develop- 

 ing" the country, each one trying to get all he could and leaving 

 the next to take care of himself. But as Gifford Pinchot puts 

 it, "Each generation has a right to all it needs, but no right 

 whatever to waste what it does not need. Our children have 

 their rights as well as we." It was under ]\Ir. Pinchot's influ- 

 ence that President Roosevelt became the strong promoter of a 

 national conservation policy. 



THE EARTH FOR MANKIND 



1. Interdependence of living things 



Chlorophyl the basis of life Food relations 



Oxygen cycle Decay and scavenger feeding 



Carbon-dioxid cycle Parasitic feeding 



Nitrogen cycle Predatory feeding 



2. Struggle for existence 



Life feeds upon life 

 Protoplasm destroyed in course of its activity 

 Protoplasm of others destroyed in growth 

 Reproduction in excess of means of subsistence 

 Struggle not a conscious or painful process for the most part 

 Directions of struggle 

 External conditions 



Temperature Chemical conditions 



Moisture Air 



Light Water 



Soil 



