the Caucasian and Mongolian races, the different varieties of "Wheat 

 and Barley have been cultivated from times immemorial, and the 

 former, especially, has transported them into every country it has 

 penetrated, where the temperature is neither too high nor too low 

 for their development ; where the first is the case, Rice and Millet 

 constitute the vegetable diet of these races, as well as those of the 

 Negro and Malay. The Maize, or Indian-corn, although long 

 since introduced by European commerce into various parts of the 

 eastern continent, was unknown by us until the discovery of 

 America, where, like the Wheat and Barley, it was only met with 

 under cultivation, and distributed along a line which tradition has 

 recorded as the tract of the Toltecs ; a tribe probably of Asiatic 

 origin, that, migrating from the north-west to the table-land of 

 Mexico, and penetrating far into the southern peninsula, laid the 

 foundation of regular government, and the advanced state of 

 civihzation found by the Spaniards on their arrival at the countries 

 in question. 



The agricultural associations of all these kinds of Corn, as af- 

 fected by climate and other circumstances, are among the most 

 important facts appertaining to the history of the tribe of plants 

 before us. The necessary limits of this introduction will not ad- 

 mit of details; but a few short extracts from Schouw, a Danish 

 writer on the geographical distribution of plants, as published some 

 years back in Jameson's Edinburgh Journal, will furnish sufficient 

 information on the point in question to satisfy the general reader : 



"Within the northern polar circle, agriculture is only found in 

 a few places. In Siberia, grain reaches at the utmost only to the 

 latitude of 60°; in the eastern parts, scarcely above 55°; and in 

 Kamtschatka there is no agriculture. Only in Europe, namely in 

 Lapland, does the polar limit of agriculture reach an unusually 

 high latitude, 70°. The grains which extend farthest to the north 

 of Europe are Barley and Oats. These, which in the milder cli- 

 mates are not used for bread, afford to the inhabitants of the 



