324 OiSMOs. 



difference, and to the unmeasured heat which is locally devel- 

 oped in the living vegetable cell by the action of direct light. 

 If, in forming a thermic scale of different kinds of cultiva- 

 tion,* we begin with those plants which require the hottest 

 climate, as the vanilla, the cacao, banana, and cocoa-nut, and 

 proceed to pine-apples, the sugar-cane, coffee, fruit-bearing 

 date-trees, the cotton-tree, citrons, olives, edible chestnuts, and 

 vines producing potable wine, an exact geographical consider- 

 ation of the limits of cultivation, both on plains and on the 

 declivities of mountains, will teach us that other climatic re- 

 lations besides those of mean annual temperature are involved 

 in these phenomena. Taking an example, for instance, from 

 the cultivation of the vine, we find that, in order to procure 

 potable wine,t it is requisite that the mean annual heat should 

 exceed 49^, that the winter temperature should be upward of 

 33^, and the mean summer temperature upward of 64^. At 

 Bordeaux, in the valley of the Garonne {4.\P 50' lat.), the 

 mean annual, winter, summer, and autumn temperatures are 

 respectively 57*^, 43^^, 71°, and 58^. In the plains near the 



alia est caloi'is vis, quern radii solis nuUis nubibus velati, in foliis ipsis 

 et fructibus maturescentibus, magis minusve coloratis, gignunt, quem- 

 que, ut egregia demonstrant experimenta amicissimorum Gay-Lussacii 

 et Thenardi de combustione chlori et hydrogenis, ope thermometri me- 

 tiri nequis, Etenim locis planis et montanis, vento libe spirante, cir- 

 cumfusi aeris temperies eadem esse potest coelo sudo vel nebuloso ; ide- 

 oque ex observationibus solis thermometricis, nullo adhibito Photome- 

 tro, baud cognosces, quam ob causam Galliae septentrionalis tractus 

 Armoricanus et Nervicus, versus littora, coelo temperato sed sole raro 

 utentia, Vitem fere non tolerant. Egent enim stirpes non solum caloris 

 stimulo, sed et lucis, quae magis intensa locis excelsis quam planis, du- 

 plici modo plantas movet, vi sua turn propria, tum calorem in superficie 

 earum excitante." — Humboldt, De Distributione GeograpMca Planta- 

 rum, 1817, p. 163-164. 



* Humboldt, op. cit., p. 156-161; Meyen, in his Grundriss der 

 Pjlanzengeographie, 1836, s. 379-467 ; Boussingault, Economie Rurale, 

 t. ii., p. 675. 



t The following table illustrates the cultivation of the vine in Europe, 

 and also the depreciation of its produce according to climatic relations. 

 See my Asie Centrale, t. iii., p. 159. The examples quoted in the text 

 for Bordeaux and Potsdam are, in respect of numerical relation, alike 

 applicable to the countries of the Rhine and Maine (48'^ 35' to 50*^ 7' 

 N. lat.). Cherbourg in Normandy, and Ireland, show in the most re- 

 markable manner how, with thermal relations very nearly similar to 

 those prevailing in the interior of the Continent (as estimated by the 

 thermometer in the shade), the results are nevertheless extremely dif« 

 ferent as regards the ripeness or the unripeness of the fruit of the vine, 

 this difference undoubtedly depending on the circumstance whether 

 the vegetation of the plant proceeds under a bright sunny sky, c un 

 der a sky that is habitually obscured by clouds: 



