CHAPTER XXII 

 THE SMELT: A STUDY OF FOOD SUPPLY 



Green plants only can transform inorganic substances into 

 living matter with the aid of the energy of the sun. Yet it is 

 upon such inorganic substances that all living matter eventu- 

 ally depends for its increase, and it is from solar energy that 

 all vital energy sooner or later comes. Accordingly, animals, 

 including man, must get their energy either from plants or 

 from plant -devouring animals. 



The total amount of energy derived from the sun is enor- 

 mous. On the land this energ\' is absorbed by forests, by the 

 grasses of prairies and meaflows, and by growing crops ; and 

 is by them transformed into new, living material. Alan is 

 constantly working to increase the proportion of solar energy 

 that becomes fixed in the crops, but onh' a verj- small propor- 

 tion of the surface of the land is yet under cultivation. There 

 are great tracts, such as deserts and rocky places, where the 

 falling energy seems to be ciuite wasted, and the same seems 

 to be true of the water surface of the earth, which amounts to 

 three-fifths of the whole (Fig. 282). It is, however, very far 

 from the truth that the solar energy falling on the sea is lost, 

 for the entire surface of the sea swarms with microscopic green 

 organisms which are to the sea what the grass of the fields is 

 to the land. The green plants of the ocean are the food of the 

 small Crustacea called Entomostraca (p. 156), and these, 

 as we saw in Chapter X, in turn are the food of fishes. In 



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