1274 



AMERICAN FORESTRY 



great that they cover large sections of whole continents. 

 The best known but not the only examples of the latter 

 are the grasses of the North American prairies, the con- 

 ifers of our evergreen forests, and the broad-leaved trees 

 of our great deciduous forest. 



The heart of the great deciduous forest was the Ohio 

 Valley. This forest consisted of an association of many 



THE SHOWY ORCHID 



One of tlie most beautiful flowers and readily identified as an orchid by 

 its characteristic odor and taste, differentiating this class from all 

 other plants. 



species, and a century ago, it stretched almost without a 

 break from the Atlantic Coast to Western Minnesota. 



North of this broad-leaved forest extended a belt of 

 evergreens to the limit of trees into sub-arctic regions and 

 westward to the treeless plains. This vast forest con- 

 sisted however of comparatively few species. In its 

 southern region the white and Norway pines were the 

 dominant trees. They grew taller and lived longer than 

 any other species, and where fires or storms had not 

 interfered for a century or two they had crowded out, 

 or at least suppressed every other kind. 



Farther north, especially on poorly drained lands, the 

 black spruce becomes dominant, while vast swamps, too 

 wet for the spruce, are covered with tamarack, which on 

 better and higher land was crowded out by pines, spruces 

 and other species. 



From Illinois to the foothills of the Rocky Mountains 

 stretched the largest grassy meadows of the world, known 

 as the prairies. 



The question why these great fertile regions re- 

 mained treeless is not easily answered. Over a 

 part of the prairies the rainfall is insufficient to meet 

 the great demands of trees for water. For con- 

 trary to the popular idea, forests do not cause rain- 



fall, but an abundant rainfall makes forests possible. 



However, over a large part of the prairies other fac- 

 tors have operated against the spread of trees. The 

 grasses developed early in the geological history of North 

 America, and when the plains first emerged from the 

 sea, the grasses were able to cover the soil before the 

 trees could reach the new land. The compact unbroken 

 sod formed by their roots made it difiicult for trees to 

 secure a footing, but wherever the soil was broken by 

 streams and the waves and ice of lakes, trees and shrubs 

 have successfully invaded the great plains and now fringe 

 every lake and river. 



Nearly all the prairie grasses and flowers are perennials 

 well fitted to resist aimual or occasional severe droughts. 

 Nor could millions of grazing buffaloes and the fires 

 started by lightning or by primitive man harm the under- 

 ground rootstock of these plants. To seedling trees, 

 however, a fire means almost certain destruction. 



On the western plains in the Bad Lands region and in 



SKUNK CABBAGE-FIRST FLOWER OF THE NORTHERN ST.'iTES 



AND CANADA 



The large seeds Iiavc most likely been scattered by bears. 



the foothill country the short grasses are rendered still 

 more drought-resistant by having their roots protected 

 by hard impervious sheaths. These grasses produce the 

 black-root sod, which western ranchers and pioneers em- 

 ploy as building material, and the walls constructed of 

 black-root sod are almost as durable as those built 

 of brick. 



Leaving out of consideration here the rather complex 

 problem of plant distribution over the Black Hills, the 

 Rocky Mountains and the Great Basin we reach on the 



