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On the Hombothermal method of Acclimating [April 



than that in which it is to grow (the very change which it is the object 

 of the Homoothermal method to produce), to prepare it for culture in a 

 tropical climate, by rendering it so very susceptible of cold, that a 

 slight reduction of temperature is sufficient to counteract the injurious 

 tendency of excessive heat. According to this view it is desirable that 

 the authors of the memoir should extend and vary their experiments, 

 so as to determine this point, and prove the existence of the modifying 

 principle I have supposed. This, with the experience derived from 

 their former experiments, might now perhaps be more easily accom- 

 plished than it could have been previously. They have ascertained 

 that winter wheat, sprouted under a temperature of 19° centigrade, and 

 exposed to temperatures progressively increasing to 22, did not succeed; 

 let them now sprout the same variety in a heat of 23 or 25°, and after it 

 has ceased to grow erect, expose it to the highest summer heat of 

 France (22), that at which all varieties of grain yet tried had failed, and 

 see whether it will then throw out new fruitful shoots, as the others 

 had done on the reduction of temperature ; and, in the event of its per- 

 fecting its seeds, to ascertain whether they can successfully contend 

 with such a temperature as arrested the progress of the parent stock. 

 Until some such course as that here suggested is adopted, the experi- 

 ments hitherto made can be of no value to agriculture, opposed as they 

 are by unlimited experience in warm climates. Humboldt who had 

 no such theory to support, and who therefore simply states the facts as 

 either known to himself or recorded by others, writes as follows. 



" The environs of La Victoria present a very remarkable aspect, 

 w 7 ith regard to agriculture. The height of the cultivated ground is 

 from two hundred and seventy to three hundred toises above the level 

 of the ocean, and yet we there find fields of corn mingled with planta- 

 tions of sugar-canes, coffee, and plantains. Excepting the interior of 

 the island of Cuba,* we scarcely find any where else in the equinoctial 

 regions European corn cultivated in large quantities in so low a region. 

 The fine fields of wheat in Mexico are between six hundred and twelve 

 ihundred toises of absolute elevation ; and it is rare to see them descend 

 to four hundred toises. We shall soon perceive, that the produce of 

 grain augments sensibly, from high latitudes toward the equator, with 

 the mean temperature of the climate, in comparing spots of different 

 elevations. The success of agriculture depends on the dryness of the 

 air ; on the rains distributed among different seasons, or accumulated 

 in one rainy season ; on winds blowing constantly from the east, or 

 bringing the cold air of the north into very low latitudes, as in the gulf 

 of Mexico ; on mists, which for whole months diminish the intensity of 

 the solar rays ; in short, on a thousand local circumstances, which have 



* The district of Quatro Villas, 



