AMERICAN INSTITUTE. 589 



abounding with those substances, they can never be developed. 

 The reason why the pine tree grows, in preference to all other 

 trees, on the worn out lands of Virginia, is, that the salts of potash 

 have been removed by the tobacco culture, and pines requiring 

 less than other indigenous trees, flourish. 



All plants must have a definite quantity of heat from the com- 

 mencement of their germination to the end of their organic 

 activity. On the banks of the Nile, barley is sown on the first of 

 December, and is harvested in ninety days. The mean tempera- 

 ture during that period is 69° 48'. In Tuqueres, nearly under 

 the equator, they sow the last of May, and harvest on the fifteenth 

 of November. The mean temperature of this growing season, 

 (168 days,) is 50° 12'. At Bogota, the growing season requires 

 about 123 days, and the mean temperature is 57° 24'. The 

 same results have been obtained with wheat, corn, rye, potatoes, 

 &c. From this statement we deduce the fact, that all plants 

 require a certain quantity of heat for their development; but it 

 does not matter whether it is distributed over a long or short 

 space of time. 



There was a period when the temperature throughout the 

 world, from pole to pole, was uniform, as is conclusively proved 

 by the growth of plants; as discovered in the coal formations. 

 This was called the carboniferous era. And as the carbonic acid 

 gas was consolidated into coal, great changes were uniformly 

 impressed upon the atmosphere, and our numerous climates were 

 formed under the influence of the sun. Then animals and plants 

 became localized within certain temperature barriers, each hav- 

 ing its own special fauna and flora. Those of Africa are distinct 

 from Europe; Europe from America, and America from New- 

 Holland. And what is more remarkable still, the variety of 

 man is homogeneous with the flora and fauna. The Africans 

 are black, and originated, probably, from a lusus naturae, as do 

 the Albinos; the Mongolians yellow, Europeans white, and 

 Americans red. The coloring matter In the skin of the three 

 last named, is so slight that it is probably developed by the influ- 

 ence of temperature and climate operating upon the liver, as it 

 grows dark toward the equator, and light toward the poles. We 



