46 FORESTS AND MANKIND 



hardly perceptibly, so the trees are changing. Behind the veil 

 of the future may lie tree forms of which man has never 

 dreamed, higher forms still better equipped to live and multi- 

 ply. For that is the way life seems to be working, always 

 toward organisms that will carry the spark of life safely on 

 and perpetuate it in the face of adverse conditions. 



But not to tree species alone are these forest changes con- 

 fined. Tree areas, too, are shrinking and expanding today no 

 less than in the remote past. Forests are invading the desert 

 in one region and retreating before adverse conditions in an- 

 other. The cypress, for example, last living representative of its 

 race, seems to be slowly shrinking in its area of distribution. 

 Others are thrusting their boundaries forward seizing ground 

 once held by other species. 



The species of our older trees have become less numerous. 

 Once the sun never set on the liriodendron, that magnificent 

 tree we variously call tulip tree, tulip poplar, yellow poplar, 

 and white wood. It grew once in all parts of the globe and at 

 least nine different species have been found. Now there are 

 only two species left, one in America and the other in far-off 

 China. From the rest of the world the tulip tree has vanished 

 utterly. So it seems that the older forms die and new ones take 

 their place. Changing conditions changing forms. 



And although in our modern forest we have here and there 

 isolated types like the sequoia, successful survivals that have 

 held their own in spite of ceaseless change, still the woods of 

 today are quite different from those of other days and these 

 too are constantly changing. Only a few, the sequoia, ginkgo, 

 and one or two others remain like vestiges of the remote past 

 to link our forests of today with the forests of long ago. 



