294 On the Hombothermal method of Acclimating [ApRit 



rior limit a medium temperature of 25° cent. (77° Faht.), and at its su- 

 perior boundary a mean heat of 18. 8 cent. (66 Faht.) : it therefore has 

 a higher temperature than that at which the 'inhabitants can successfully 

 cultivate these grains ; a result according accurately with the deduc- 

 tions from experiment. Humboldt remarks that the temperate region 

 of all climates, where the mean annual heat is between 18 and 19° cent, 

 appears the most favourable for the culture of the Cerealise ; that in the 

 equinoctial part of Mexico the European Cerealise are not cultivated on 

 any part of the table-land, under an elevation of 8 or 900 metres (say in 

 round numbers 2600 and 3000 feet) ; and on the slopes of the Cordillier- 

 as, between Vera Cruz and Acapullo, he had rarely seen that kind of 

 cultivation commence under an elevation of 12 or 13 hundred metres. 

 That long experience had proved to the inhabitants of Xalapa that 

 wheat, sown about that town, vegetates vigorously, but does not shoot 

 upwards into ear ; on which account it is cultivated as pasture and 

 forage for cattle: but that, in the province of Guatimala, though much 

 nearer the equator, and at a lower elevation, European corn ripens ; 

 perhaps owing to some local cause modifying the influence of the cli- 

 mate. He further informs us that he has seen, in the province of 

 Caraccas near Victoria (latitude 10° 13'), the most beautiful fields of 

 wheat, at an elevation of from 17 to 19 hundred feet ; that the corn 

 fields of the isle of Cuba (lat. 21. 58) have even a less elevation than 

 that ; and in the Isle of France (lat. 20° 10') wheat is cultivated almost 

 at the level of the sea. 



These last statements seem so greatly at variancewith the facts pre- 

 viously enumerated and the deductions from them, that it is diffi- 

 cult to conceive how they can be reconciled, or reduced to any general 

 principle, otherwise than by assuming that culture can produce 

 varieties suited to different climates. Would the Victoria, Cuba, 

 and Mauritius varieties of wheat succeed in France, if sown during the 

 summer season, or in circumstances similar to those in which the win- 

 ter and spring varieties of that country had failed ? I think they would. 

 The cultivation of wheat in this country affords an additional proof in 

 support of this view, and the recent presentation at the meeting of the 

 Madras Agricultural Society of well filled ears of the Victoria variety of 

 wheat, and also of barley and oats, all grown in a mean temperature of 

 about 75°j confirms it; since all the European varieties of the same kinds 

 of grain failed in France, under a mean temperature not exceeding 71 

 degrees. 



Perhaps these differences may be more satisfactorily accounted for 

 on the principles explained in my former paper, and even the cause 

 of the production of varieties shown. Thus it was observed, in the 

 course of the experiments in France, that the growth in a normal forra r 



