HORTICULTURAL JOURNAL. 219 



where it rises above 71° 36' Barley will no longer ripen. Consequently, to 

 Afine accurately the conditions of temperature which a plant requires to 

 maintain it in a flourishing condition, we must state within what limits its 

 period of vegetation may vary, and what quantity of heat it requires. This 

 most remarkable circumstance was first observed by Boussingault, but unfor- 

 tunately, we as yet possess not nearly sufficiently accurate accounts of the 

 conditions of culture, in the various regions of the earth, to enable us to 

 follow out this ingenious view in all its details. 



I have chosen the Barley as an example in the preceding remarks, be- 

 cause it has the widest range of distribution of all the Cerealia, and is culti- 

 vated from the extreme limits of culture in Lapland, to the heights imme- 

 diately beneath the equator. But it has by no means the same importance 

 everywhere that it has in the northern region, where, in a little narrow 

 zone, it appears as the sole bread-corn ; and in the following observations 

 on the distribution of the more important Cerealia, it will be considered 

 only in reference to this last point. In Lapland and northern Asia, Bye 

 soon appears beside it, but by the inclemency of the climate confined to fa- 

 vorable years, and therefore not properly to be regarded as the principal 

 food. First in Norway, Sweden, Finland, and Russia, does the Bye be- 

 come the peculiar bread-corn ; and Wheat takes its place beside it in the 

 north of Great Britain and Germany, as the Rye before joined Barley. 

 In the centre of Germany, in the south of Great Britain, in France, and 

 in a wide range toward the East, including the whole of the Caspian Sea, 

 Wheat is the prevailing cultivated plant, which, in the basin of the Medi- 

 terranean and throughout North America, is associated with Maize. Rice 

 takes the place of the latter in Egypt and in northern India, and holds 

 undisputed rule in the peninsulas of India, in China, Japan, and the East 

 Indian Islands, shares it in the west coast of Africa with Maize, which, on 

 the other hand, is the exclusively cultivated corn-plant of the greatest part 

 of tropical America, with only some unimportant exceptions. In southern 

 America, Africa and Australia, Wheat again enters the field, with the de- 

 creasing temperature. The culture of Tef* and Tocusso^ in Abyssinia, 

 of MiUetJ in western Africa and Arabia, as well as of Eleusine^ and Millet|| 

 in the East Indies, are quite of subordinate importance. 



Some other plants bear a far more important share in the nutrition of 

 mankind than the Grasses last named. Even in the most northern zone of 



* Poa Abyssinica. fEleusine Tocusso. 



% Sorghum vulgare, and others. $ Eleusine coracana and stricta. 



II Panicum frumentaceum. 



