THE CUREENTS OF THE ATLANTIC. 401 



months of June, July, and August. Now, if we look to the dis- 

 tribution of the cereals in Europe, as given by Berghaus or John- 

 stone in their physical Atlases, we observe that they are arranged 

 in belts, or zones, whose limits correspond nearly with the lines of 

 equal summer temperature. Thus we have, first, a belt of barley 

 alone, which extends from the North Cape, in latitude 70 N. to 

 about midway in Norway and Sweden. This is followed, as we 

 proceed southward, by a belt containing oats and rye, as well as 

 barley. Then comes a belt of rye and wheat, in the south of Scan- 

 dinavia, and in the north of central Europe. In the southern 

 half of Europe, we have wheat alone ; and, beyond this, wheat and 

 maize on the coasts of the Mediterranean. And the boundary lines 

 of these several districts are all related, more or less closely, to the 

 isothermal lines of mean summer temperature. 



It is of the first importance to the agriculturist to know these 

 limits in his own district ; for on their position will depend the 

 chances of successful cultivation of the particular crop. I shall 

 therefore ask your attention for a few moments longer, while I 

 endeavour to ascertain the limit of wheat, the most important of 

 the cereals, in these islands. The result of the inquiry is some- 

 what startling, and it deserves to be more fully known. 



There is some doubt still as to the native place of the cereal 

 grasses. Most of them have been found growing wild in Persia, 

 on the banks of the Euphrates, and in Tartary. Whatever their 

 original habitat may have been, it was a warmer clime than ours. 

 The mean summer temperature of the British Islands is under 60, 

 while that of the plains of Lombardy, where wheat is grown in 

 perfection, is 73 ; and that of Sicily " the granary of ancient 

 Rome " is 77. "We are, therefore, in these countries, probably 

 near the lower limit of the wheat crop, beyond which its successful 

 culture is impossible. It is important that we should know how 

 near. 



We have some of the data requisite for the determination of 

 this question, in the long series of observations of temperature 

 made at the apartments of the Eoyal Society, in London, as com- 

 pared with the prices of wheat, given for an equally long series of 

 years in " Tooke's History of Prices." From the former we learn 

 how far the summer temperature of each year deviated from the 

 mean ; while the latter furnish us with a measure of the abundance 



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