Figure II 



Our planet, showing the 

 major vegetational belts 

 girdling It but oscillating 

 and varying in width 

 due to the influence 

 of the ocean currents 



NOITMERN FOSEST 



NORTHERN 

 GRASSLANDS 



NORTHERN DESERT 

 NORTHERN savannah" 

 TROPICAL FOREST 

 SOUTHERN SAVANNAH <, 

 SOUTHERN DESERT ^ 

 SOUTHERN GRASSLANDS -V- 



SOUTHERN FOREST 



there is a further point: if will be found that these zones start and stop at different heights 

 at>ove sea level at different latitudes, and that they start at lower and lower levels as one 

 approaches the poles, so that mountains near the poles are covered with snow and ice from 

 their bases to their apices. In point of fact, each degree of latitude proves to be equivalent to 

 six hundred feet of altitude, so that a climber can calculate in advance just when he will pass 

 from one vegetational type to another — provided, of course, the latitude is known 



OCEAN CURRENTS 



These facts clearly indicate that there is some underlying order here. We would naturally like 

 to know upon what "laws" or principles this is based, so let us start by imagining that our 

 planet is without seas and oceans but that it has just the same moisture and climate that it 

 now enjoys. (This of course is impossible, even theoretically.) If also it should be perfectly 

 flat all over but still tilted at 23 degrees to the plane upon which it revolves around the sun, 

 what would be its phytogeographical appearance? For purposes of simplicity and explana- 

 tion, let us say that it appears as in Figure I. with all major belts encircling it latitudinally. 



However, our planet is not all land and perfectly flat, while the vegetational belts mani- 

 festly sway about to north or south, and widen or contract as we follow them around. Is there 

 any connection between these two facts, and if so is there any one cause? It turns out there 

 is a very definite connection and. surprisingly, only one basic cause. This is the distribution 

 and behavior of the major ocean currents. This force is paramount and is apparently the 

 cause not only of the nature, direction, and extent of the swings but also of other factors that 

 control the width of the belts at any one point. In fact, "climate" is basically controlled by 

 the ocean currents and is only secondarily affected by the atmospheric circulation. Altitude 

 moreover has almost nothing to do with the swings made by the major vegetational belts. The 

 actual state of affairs may be seen in Figure II, wherein the ocean currents are seen circulating 

 in their opposed manners as in the north and south hemispheres, the cold ones pushing all 

 the belts toward the equator, the hot. toward the poles. 



Given the distribution of land and the circulation of ocean currents, certain parts of eadi 

 of the continents will be dry. others wet, because atmospheric moisture comes from the oceans 

 and hot oceans evaporate faster, while the winds blowing from them carry more water than 

 do those blowing off cold oceans. The details of this need not be dwelt upon here; they are 

 mechanical; they conform to physical law; and their results all over the earth are exact. What 

 are these results on North America? 



This is shown on the general map on page 8. All the belts are pushed south far down 

 the Pacific coast, then far north just inland. From there they follow a great curve to the 

 southeast to the inner or western face of the Appalachians, then around them, and finally 

 north again up the east coast and out into the Atlantic. The pattern is exaggerated but basi- 

 cally simple. Moreover, even the greatest mountain ranges have no effect upon these swings: 

 they are just dumped down, as it were, athwart them, and partake of their own arrangements 

 of "belts" — called more properly zones when applied to altitude. 



DEFINING NORTH AMERICA 



There comes, then, the question of the definition of North America as a continent. Our theme 

 is phytogeographical and based primarily on the distribution of the various types of vegeta- 



