4. C. Pahudiana Howard.
Kuntze, who has examined the living Cinchonæ as cultivated in India, is of the opinion that all the numerous forms hitherto observed, both in the wild plants and in cultivation, are merely either belonging to the above four species or deriving from them chiefly by hybridation. Though much in favour of a reduction of the species, we are not yet prepared to accept Kuntze’s arrangement.
(B.) Area, Climate and Soil.—The Cinchonas are natives of South America, where they occur exclusively on the western side of the continent between 10° N. lat. and 22° S. lat., an area which includes portions of Venezuela, New Granada, Ecuador, Peru, and Bolivia.
The plants are found in the mountain regions, no species whatever being known to inhabit the low alluvial plains. In Peru and Bolivia, the region of the Cinchona forms a belt, 1300 miles in length, occupying the eastern slope of the Cordillera of the Andes.[1288] In Ecuador and New Granada, the tree is not strictly limited to the eastern slopes, but occurs on other of the Andine ranges.
The average altitude of the cinchoniferous region is given by Weddell as 5,000 to 8,000 feet above the sea-level. The highest limit, as noted by Karsten, is 11,000 feet. One valuable species, C. succirubra, occurs exceptionally as low as 2,600 feet. Generally, it may be said that the altitude of the Cinchona zone decreases in proportion as it recedes from the equator, and that the most valuable sorts are not found lower than 5,000 feet.
The climate of the tropical mountain regions in which the Cinchonas flourish, is extremely variable,—sunshine, showers, storms, and thick mist, alternating in rapid succession, yet with no very great range of temperature. A transient depression of the thermometer even to the freezing point, and not unfrequent hail-showers, may be borne without detriment by the more hardy species. Yet the mean temperature most favourable for the generality of species, appears to be 12 to 20° C. (54 to 68° F.)
Climatic agencies appear to influence the growth of Cinchona far more than the composition of the soil. Though the tree occurs in a great variety of geological formations, there is no distinct evidence that these conditions control in any marked manner either the development of the tree or the chemical constitution of its bark. Manure on the other hand, though not increasing perceptibly luxuriance of growth, has a decided effect in augmenting the richness of the bark in alkaloids.[1289]
(C.) Species yielding officinal barks.—The Cinchona Barks of commerce are produced by about a dozen species; of these barks the greater number are consumed solely in the manufacture of quinine. Those admitted for pharmaceutical use are afforded by the following species:—
1. Cinchona officinalis Hooker[1290]—A native of Ecuador and Peru, existing under several varieties. It forms a large tree, having lanceolate or ovate leaves, usually pointed, glabrous, and shining on the upper surface, and scrobiculate on the under. The flowers are small, pubescent and in short lax panicles, and are succeeded by oblong or lanceolate capsules, ½ an inch or more in length.
2. C. Calisaya Weddell—Discovered by Weddell in 1847,[1291] although its bark had been an object of commerce since the latter half of the previous century.