IN a previous chapter I have given an account of the arrangements which I made for procuring the various species of Chinchonæ in districts other than that of the Calisaya, and it now remains for me to record the labours of those whom I employed on this service, and the successful results with which those labours were rewarded. And first, both in importance and success, stands the expedition of Mr. Spruce, to collect the seeds and plants of the "red-bark" tree or _C. succirubra_, of whose services it would be impossible to speak too highly. I may mention, at starting, that he received my first letter, requesting him to undertake the work, on July 2nd, 1859, and such was his zeal that on the 22nd of the same month he was on his way to the chinchona forests, at his own expense, to ascertain the best locality for collecting the plants and seeds. The species of chinchona, known as the "red-bark" tree, yields a larger per-centage of febrifugal alkaloid than any other, and must therefore be considered as the most important.[367] Its native forests are on the western slopes of the famous mountain of Chimborazo, in the Republic of Ecuador, and for a great many years it has not been found beyond 2° 36´ S. lat., but Mr. Spruce thinks it probable that in former times the tree grew all along the roots of the Andes of Cuenca and Loxa to the limits of the Peruvian desert in 5° S. To the north it scarcely passes the latitude of 1° S.; and these precious trees are thus confined within a very narrow latitudinal zone.[368] Within the ascertained limits of the true "red-bark" tree, it exists in all the valleys of the Andes which debouch on the plain of Guayaquil; but great havoc has been made amongst the trees of late years by the bark-collectors. In the valleys of Alausi, Pallatanga, and Chillanes (see map) all the large trees have already been cut down. At the bases of the ridges of Angas and San Antonio, the localities originally mentioned by Pavon, and where "red-bark" trees once grew in abundance, the same destructive system has been adopted; and now the "red-bark" grounds are confined to the ravine of the river Chasuan, and its tributaries, which rise on the northern slopes of Chimborazo, and fall into the river of Guayaquil.