478 AGRICULTURAL REPORT. 



tcmpcratnrc due to the surrounding water. At Moscow, wliere tlic plant appearp, 

 the sum exceeds the supposed condition, and the Euonjjtnus doubtless extends 

 here further north. Finally, at Kazan this figure is reduced to 2,250^, and here 

 the plant does not appear. The values thus found along the limit in its neigh- 

 borhood, and beyond it, accord as nearly as could be desired with the double 

 hypothesis of a minimum of 6^ centigrade, and an aggregate temperature for 

 the growth and maturation of Euonymus Europcetis of about 2,480° centi- 

 grade. 



De Candolle considers himself justified, by the results derived from the in- 

 vestigation of the limits of the northern extension of nearly forty species of 

 plants, to enxmciatc the law of nature that " every species having its polar 

 limit in central or northern Europe advances as far as it finds a certain fixed 

 amount of heat, calculated from the day when a certain mean temperature 

 commences to the day Avhen that mean terminates." The apparent exceptions 

 to this rule may be explained by two circumstances which restrict its applica- 

 tion. The eastern and western limits of a species may be determined by the 

 humidity or dryness of portions of the region over which it would otherwise 

 extend, or perennial and woody plants are sometimes arrested in their exten- 

 sion towards the north by the absolute minima of temperature. In tracing a 

 limit of a species from east to west, if the law as stated ceases to be applicable, 

 the species may be supposed to have encountered the excluding influence of 

 severe cold or excessive drought or humidity, and it is often difficult to decide 

 which of these causes operates as an obstacle. 



THE TEMPERATURE AFFECTING THE VINE. 



There are few crops that are so much at the mercy of the atmosphere and its 

 varying conditions as that derived from the vine. Even in vineyards that are 

 most favorably situated, it is rare that wines of equal quality and flavor are 

 produced in two consecutive yeai's; and in districts upon the verge of the pro- 

 ductive limits of the vine under extreme climates, where it exists only in virtiie 

 of hot summers, its produce is still more variable, more inconstant. 



The limits to the culture of the vine in Europe are generally fixed where the 

 mean annual temperature is from 50° to 52°. Under a colder climate in Europe 

 no potable wine is produced. To this meteorological datum must be added the 

 fact that the mean heat of the cycle of vegetation of the vine must be at least 

 59° Fahrenheit, and that of the summer from 0)5° to G6° Fahrenheit. Any 

 country which has not these climatic conditions cannot have other than indif- 

 ferent vineyards, even when its mean annual temperature exceeds that above 

 indicated. It is impossible, for instance, to cultivate the vine upon the tem- 

 perate table lands of South America, Avhere they nevertheless enjoy a mean of 

 from G2.G° to 66.2° Fahrenheit, becajise these climates are characterized by 

 constancy of temperature, never rising to the higher heats necessary to the 

 process of sugar-forming, and the vine grows, flourishes, but the grapes never 

 become thoroughly ripe. Even in Europe, where the climate partakes of a 

 regularity that to U3 is remarkable, the varying temperature of the summer 

 mean from year to year jjroduces a corresponding variation in the quality of 

 the wine. This quality may, in good measure, be tested by the amount of 

 alcohol contained therein, as this is directly as the amount of sugar elaborated 

 by the heat of the summer months, or by the epoch of its growth, during which 

 the sugar-forming process takes place. 



4- series of observations, from 1833 to 1837, inclusive, made in Flanders, 

 shows the following results, which may be better understood if placed in a tab- 

 ular form : 



