THE WONDERS OF VEGETATION. 17 



exercises any thing like the degree of influence which 

 this agency brings to bear upon the distribution of 

 plants. 



Let us for an instant consider the world as a sphere 

 turning upon its axis an ideal line passing through 

 its centre and call the two points where this line 

 would reach the surface as respectively the North and 

 South poles. The motion at the poles will of course 

 be inappreciable. We will give the name of the equa- 

 tor to the great ideal circle which passes round the 

 middle of the earth, dividing it into two equal halves 

 the North and South hemispheres. Now, as the 

 rays of the sun are so much the more oblique the more 

 they diverge from the equator, it follows that the heat 

 at the equator is at the maximum while at the poles it 

 is at the minimum. With the decrease of heat from 

 the equator toward the poles corresponds the geograph- 

 ical distribution of plants. At the equator and in the 

 neighboring tropical regions we meet with the vast 

 proportions of the largest plants as the boababs, the 

 palms, the elegant tree-ferns, the aloes, the heaths- 

 magnificent plants which love and seek heat. In leav- 

 ing these heated countries we encounter olives, laurels, 

 mimosas and bamboos. Continuing our route towards 

 the poles we see magnolias, chestnut-trees, cotton plants 

 and witchelms. Proceeding still further from the 

 tropics till we reach the latitude of France and Mid- 

 dle Europe, or our Middle and Eastern States, we 

 meet with oaks, beeches, willows and elms, with our 

 common fruit-trees and our cereals. In the Nor- 

 thern countries, near the limits of vegetation, we 

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