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Rh this part of the subject with interest. It is my own belief, that no general theory can be established; for, as I have stated in the first section, a thousand local causes, totally independent of elevation, may, and do, produce the degree of heat required to bring the cane to perfection. It is admitted, however, that the juice is more, or less, abundant, and rich in saccharine matter, in proportion to the height at which it is grown; and that the produce of a plantation in a valley on the Table-land, would not be equal, either in quality, or quantity, to that of a plantation of similar extent upon the coast.

Elevation has, therefore, some peculiar effects upon vegetation, even where external appearances are the same; but to what extent, and in what way its influence is exercised, it remains for future naturalists to determine. In general, it is thought that the sugar-cane requires a mean temperature of 19 or 20 degrees of the centigrade thermometer, (68 or 69 of Fahrenheit). Mexico possesses upon her Eastern and Western line of coast, a vast extent of country in which this temperature may be found; but as exportation was only permitted, before 1810, through the port of Veracruz, while the great body of consumers was concentrated on the Table-land, but little attention was paid to those situations, which were not within reach of one of these markets.

It is to the constancy of the demand in the Interior, that we must attribute the choice of the valleys