distribution from New Brunswick to Florida and westward beyond the 

 Rockies, forming with the equally frugal Aspen and Cottonwoods the very 

 foremost advance guard of the forest. 



The skirmish line of first comers, different ones in different climates, 

 frugal in their needs, prepare the conditions for the more fastidious birches, 

 elms, maples, ashes, oak, hickories, magnolias, spruces, firs, pines, and the 

 whole host of the varied forest flora. Which of these will occupy certain 

 territory depends in the first place on temperature conditions, and in the 

 second place on moisture conditions of air and soil and the various combin- 

 ations of these factors, which determine the geographical distribution of 

 species. 



As far as temperature is concerned, there is no highest limit, provided 

 sufficient moisture be present. The forest of the tropics gives evidence of 

 this fact. On the other hand, low temperature extremes set a limit to tree 

 growth, as the northern tundras and the well-known timberline of high 

 mountains show, varying in altitude according to latitude, i.e., temperature 

 conditions. 



As regards moisture, we have seen that many species live in the 

 swamps of the South, with their feet in water for months, and their heads 

 in a humid atmosphere all the year, while the plains and deserts, deficient 

 in soil moisture and humidity of the air, are treeless, or at least forestless. 

 Within these extremes we find species adapted to every clime and site. 



As we go from the tropics to the pole, there is a change in the type of 

 the forest with each change of climate. From the evergreen, broad-leaved 

 forest of the tropics and subtropics, we may journey northward through 

 the deciduous leaved forests of the Carolinas and Pennsylvania, of oaks, 

 hickories, chestnut and tulip tree, or traveling along the Pacific Coast, 

 through a mixed forest of firs, spruces, pines, in most magnificent develop- 

 ment. Then (continuing our journey on the Atlantic side) we reach the 

 Northern forest, in which maple, beech and birch are predominant, with 

 spruce and white pine intermixed. Beyond, the number of species de- 

 creases, and generally coniferous growth predominates ; finally only eight 

 hardy species can take a stand against the frigid breath and icy hands of 

 Boreas. 



Finally, we reach beyond the 62 of latitude in the interior of Canada 

 in Alaska, much further north the last outposts, short, tousled and 

 dwarfed, the Exquimaux of tree growth. Then the treeless tundra 

 is reached, where ice and snow abound all the year, the home of 

 winter. Here the soil is frozen for all but two months in the year, when 

 only a low vegetation of willow and birch and of flowers can subsist. Just 

 as we observe these changes in a long journey, we can trace them in a day's 

 ride, if we were to ascend some mountain in the tropic or sub-tropic regions 

 of Mexico or Jamaica. We begin our journey under the palms. Again 

 we pass through the evergreen tropic forest, composed of an endless var- 



