It would be obviously out of place to enumerate in these pages all the varieties of plants, many of them of medicinal virtue, which have been introduced from Mexico into Europe. Still less can I attempt a catalogue of its flowers, which, with their variegated and gaudy colors, form the greatest attraction of our greenhouses. The opposite climates embraced within the narrow latitudes of New Spain have given to it, probably, the richest and most diversified flora to be found in any country on the globe. These different products were systematically arranged by the Aztecs, who understood their properties, and collected them into nurseries, more extensive than any then existing in the Old World. It is not improbable that they suggested the idea of those “gardens of plants” which were introduced into Europe not many years after the Conquest.[224] The Mexicans were as well acquainted with the mineral as with the vegetable treasures of their kingdom. Silver, lead, and tin they drew from the mines of Tasco; copper from the mountains of Zacotollan. These were taken not only from the crude masses on the surface, but from veins wrought in the solid rock, into which they opened extensive galleries. In fact, the traces of their labors furnished the best indications for the early Spanish miners.[225] Gold, found on the surface, or gleaned from the beds of rivers, was cast into bars, or, in the form of dust, made part of the regular tribute of the southern provinces of the empire. The use of iron, with which the soil was impregnated, was unknown to them. Notwithstanding its abundance, it demands so many processes to prepare it for use that it has commonly been one of the last metals pressed into the service of man. The age of iron has followed that of brass, in fact as well as in fiction.[226] They found a substitute in an alloy of tin and copper, and, with tools made of this bronze, could cut not only metals, but, with the aid of a silicious dust, the hardest substances, as basalt, porphyry, amethysts, and emeralds.[227] They fashioned these last, which were found very large, into many curious and fantastic forms. They cast, also, vessels of gold and silver, carving them with their metallic chisels in a very delicate manner. Some of the silver vases were so large that a man could not encircle them with his arms. They imitated very nicely the figures of animals, and, what was extraordinary, could mix the metals in such a manner that the feathers of a bird, or the scales of a fish, should be alternately of gold and silver. The Spanish goldsmiths admitted their superiority over themselves in these ingenious works.[228]