The Spanish botanists Ruiz and Pavon also examined the chinchona-trees of Loxa; and the latter described two species, _C. Uritusinga_, named from the mountain on which it was once most abundant, and _C. Chahuarguera_, so called from a fancied resemblance of the bark to a pair of breeches (_huara_ in Quichua) made from the fibre of the American aloe (_chahuar_). To these the botanist Tafalla added the _C. crispa_. These three species are all included in Humboldt's _C. Condaminea_, which is readily known by the little pits, bordered with hairs, at the axils of the veins on the under side of the leaf. It would appear that at one period of growth these little pits or scrobicules are wanting, but when the plant is in full vigour they are markedly prominent. The _C. Chahuarguera_[41] is described by Pavon as growing from eighteen to twenty-four feet in height; although now the trees, which yield the Loxa bark of commerce, do not attain a height of more than four to nine feet. It is met with on the grassy open crests of mountain ridges, in light sandy soil interspersed with rocks, amongst shrubs and young plants. The barks of Loxa were called _crown barks_, because they were reserved for the exclusive use of the royal pharmacy at Madrid; and they originally sold at Panama for five and six dollars, and at Seville for twelve dollars the pound; but in later times they were much adulterated, and the price fell to one dollar the pound. The _C. Chahuarguera_ is the _rusty crown bark_ of commerce,[42] and the _C. crispa_ is the _quina fina de Loxa_ or _crespilla negra_ of the natives. A parcel of it has quite recently sold at a higher price than _Calisaya_ quills. With this _rusty crown bark_ are mixed larger quills particularly rich in the alkaloid called chinchonidine.[43] The _C. Uritusinga_ grew to the height of a lofty forest tree, but it is now nearly exterminated. The leaves assume a red colour before they fall, acquiring the most beautiful tints, and the tree is one of the finest in those forests.[44] It is said that there is a great difference in the bark, according as it is grown on the sides of mountains most exposed to the morning or evening sun; and its position is believed to have a great influence on the quality of its alkaloids. The usual yield of the large quills is 3.5 to 3.6 per cent.[45]