324 WHEAT AND BARLEY. 



India, Arabia, Egypt, the Canary Islands, &c. Wheat can 

 be reared wherever the mean temperature of the whole 

 year is not under 37 or 39 R, and the mean summer heat, 

 for a period of at least three or four months, is above 55. 

 It succeeds best on the limits of the sub-tropical region. In 

 the Scandinavian peninsula, the cultivation of barley extends 

 to 70 N. latitude, rye to 67, and oats to 65. The cultivation 

 of rice prevails in Eastern and Southern Asia, and it is a 

 common article of subsistence in various countries bordering 

 on the Mediterranean. Maize succeeds best in the hottest 

 and dampest parts of tropical climates. It may be reared as 

 far as 40 N. and S. latitude on the American continent, on the 

 western side; while in Europe it can grow even to 50 or 

 52 of latitude. It is now cultivated in all regions in the 

 tropical and temperate zones which are colonised by Euro- 

 peans. Millet of different kinds is met with in the hottest 

 parts of Africa, in the South of Europe, in Asia Minor, and in 

 the East Indies." * 



Professor Houston furnishes the following table in illustra- 

 tion of the distribution of wheat and barley. It also shows 

 the mean temperature which they require : 



Professor Balfour's " Manual of Botany," pp. 566-568. 



