232 On the Culture of Wheat within (he Tropics. 



only exceeds the mean temperature of the three months of summer in 

 in Barbary and Egypt, both most fertile in the production of wheat, by 

 less than eight degrees of Fahrenheit. 



What the peculiar circumstances are which regulate the inferior limits 

 of corn within tlie tropics, is a problem for the satisfactory solution of 

 .which sufficient data have not yet been collected; but, as Humboldt re- 

 marks, " the fine harvests of Egypt and of the kingdom of Algiers, with 

 those of the valleys of Aragua and the interior of the island of Cuba, 

 sufficiently prove that the augmentation of heat is not prejudicial to the 

 harvest of wheat and other alimentary grain, unless it is attended with an 

 excess of drought or moisture ;" and we are not warranted in pronouncing, 

 in the absence of direct experiment, the cultivation of fields of wheat in 

 situations at this moment occupied by the most flourishing pieces of canes 

 in the low lands of Jamaica, to be impossible, were the selection of the 

 season so judiciously made, as to preclude tlie danger to be apprehended 

 from these two extremes. It is even probable that the dry and barren 

 plains of Cumana and Venezuela, which, in the intervals between the 

 rainy seasons, hardly exliibit a trace of vegetable life from the excess of 

 drought, might during the periods of the rains be brought to exliibit fields 

 of waving corn loaded with abundant ears, which the returning season of 

 drought would soon render fit for the sickle. 



We learn from Humboldt, with surprise, that while to the east of the 

 Havanna, in the famous district of Quatro Villas, the inferior limit of wheat 

 descends nearly to the level of the ocean ; to the west of the same point, 

 on the slope of the mountains of Mexico and Xalappa, the luxury of vege- 

 tation is such, that, at an elevation of six hundred and seventy-seven 

 toises, or four thousand three hundred and twenty-nine feet, an elevation 

 considerably greater than that at which wheat has been recently proved 

 to be capable of cultivation in Jamaica, the wheat does not form ears. 

 What the peculiar circumstances of this region are, which produce such a 

 result, it would require a local acquaintance with the spot to pronounce ; 

 but the cause of failure is probably to be sought in the excessive humidity 

 of the atmosphere from the quantity of uncleared forests, or the injudicious 

 selection of the seasons for the experiment. Something also should perhaps 

 be allowed for the redundant fertility of a soil enriched by the accumulated 

 deposits of vegetable matter during centuries of repose ; but to whichever 

 of these causes the faiiure is to be attributed, we may not unreasonably 

 conclude that, with the progress of civilization, the increase of population, 

 and the march of agriculture, these causes of failure will progressively dis- 

 appear, and the gifts of Ceres extend their blessings from the elevated 

 table lands, to those forest-clad slopes whose present luxuriance of vege- 

 tation prevents the wheat from forming ears, 



Previous to the experiments made during the present year in the island 

 of Jamaica, under the scientific auspices of the philanthropic Bancrofts 



