GENERAL BIOLOGY 



plant and animal tissue must be, somehow, as 

 constantly restored. 



Destruction of Organisms. Each year sees a 

 prodigious crop of annual plants " weeds " 

 in every vacant lot. Of course a large part of their 

 bulk is water, yet even if dried out, the accumulations 

 of a few years, if preserved, would so cover the 



PLANT TISSUES 



ATMOSPHERE 



ANIMAL TISSUES 



DECAY 



FIG. 24. Diagram of the carbon cycle in organic and inorganic nature. 



ground as to make it impossible for other plants to 

 struggle up from the soil to the light. The repro- 

 ductive capacity of nearly all animals is astonishing, 

 and the struggle for existence entails the destruction 

 of hosts of individuals every year. Yet we do not find 

 the surface of the earth cluttered with dead animals. 

 Indeed we rarely see one at all, or, if we do, it is only 

 the whitening bones which the rains are slowly wash- 

 ing away. What, then, becomes of them ? The an- 

 swer is at every hand. Wood is more resistant than 

 animal tissue, and we can everywhere observe 



