40 FORESTS AND MANKIND 



of preserving itself in the face of conditions that are forever in 

 a state of change. Sometimes these changes are so great or so 

 sudden that they overwhelm life. Usually they are extremely 

 slow and the various forms of life are constantly changing, 

 too making adaptations. One sees that a tree in the dense 

 forest will grow tall and slender to reach the light. But the 

 same kind of tree in the open spaces does not have to adapt 

 itself to this life and death struggle for light and so does not 

 grow tall. Plants of the desert country where rainfall is scarce 

 must conserve their moisture and have created special methods 

 for storing up the moisture they are able to raise from the dry, 

 reluctant soil. At the other extreme the palms in the rainy por 

 tions of South America get too much water and have produced 

 huge leaves that drain the rainfall outward and so keep the 

 water away from their roots. Both are useful adaptations. 



When conditions change too rapidly for a plant or animal 

 species to keep pace, it dies. We say it has become extinct. It 

 has failed to make corresponding changes with its changing 

 world and so falls out of the race. Many thousands of species 

 have fallen by the wayside since the dawn of time and prob- 

 ably the number of tree species that exists today is only a small 

 remnant compared with the numberless kinds that no longer 

 live. 



One may better understand the forests of today by learning 

 something of the ancestral forests that gave them birth. One 

 gains a sense of continuity down long ages of skillful adjust- 

 ments. Yet in doing this one must travel in a few pages across 

 many million years getting just a passing glimpse of the 

 changing world of past ages, and of the changing trees. If all 

 these changes seem rapid and sweeping it is only because of 



