103 
fold. In the middle temperate zones of Europe, viz., in 
France, wheat is cultivated to the height of 5,400 feet, and, 
according to De Candolle, rye is cultivated at 6,600 feet. 
The limit of corn culture on the Alps of Tyrol is at the 
height of 3,800 feet, in the Tyrolese Mountains 4,500 feet, 
and on Monte Rosa 5,880 feet. 
In Hungary, Croatia, and Sclavonia, the average produce 
is from eight to ten fold. In Europe the cultivation of wheat 
ascends above 62° north latitude ; indeed, Schouw gives 64° 
as its polar limit on the west side of the Scandinavian penin- 
sula, but remarks, that it begins to be of importance below 
60° north latitude ; and in our northern latitude of Great 
Britain, which is approaching its polar limit, its cultivation 
is attended with great expense. The soil frequently requires 
draining, fallowing, manuring, drilling, weeding, to several of 
which operations the more southern countries are strangers ; 
and, after all our endeavours, the yield depends upon the 
season in some manner not yet hitherto understood, or, as I 
before mentioned, on our reception of a certain number of 
days of a certain summer heat, that is, on the isotheral heat 
of Humboldt. 
Mr. Lawes has satisfactorily proved, in some experiments 
detailed in the Journal of the Royal Agricultural Society, 
that season alone can make a difference of one-third in the 
quantity of the crop. 
Upon the same field from whence seven unmanured crops 
had been taken, and no manure applied in any case, he found 
the difference in quantity in the years 1844, 1845, and 1846, 
to be as follows : — 
1844 
1845 | 
1846 
Bushels. 
Bushels. 
B. P. Q. 
Quantity of wheat per acre ... 
... 16 | 
23 
17 3 3 
So that the difference in quantity between the years 1844 
