The Pitayo Barks are restricted to the south-western districts of Columbia,[1342] and are usually imported in short flattish fragments, or broken quills, of brownish rather than orange colour, mostly covered with a dull greyish or internally reddish cork. The middle cortical layer exhibits but few thick-walled cells; the liber is traversed by very wide medullary rays, and is provided with but a small number of widely scattered liber-fibres, which are rather thinner than in most other Cinchona barks. The Pitayo barks are usually rich in alkaloids, quinine prevailing. Cinchona pitayensis is one of the hardiest species of the valuable Cinchonas, and is therefore particularly suitable for cultivation, which however has not yet been carried out as largely as that of either C. officinalis or C. succirubra.
In the Conspectus on the next page, we have arranged the principal species of Cinchona, with short indications of the barks which some of them afford.[1343]
Microscopic Structure—The first examination of the minute structure of Cinchona barks is due to Weddell, whose observations have been recorded in one of his beautiful plates published in 1849.[1344] Since that time numerous other observers have laboured in the same field of research.
General Characters.—These barks, as contrasted with those of other trees, do not exhibit any great peculiarities of structure; and their features may be comprehended in the following statements. The epidermis, in the anatomical sense, occurs only in the youngest barks, which are not found in commerce. The corky layer, which replaces the epidermis, is constructed of the usual tabular cells. In some species as C. Calisaya, it separates easily, at least in the older bark, whereas in others as C. succirubra, the bark even of trunks is always coated with it. In several species the corky tissue is not only found on the surface, but strips of it occur also in the inner substance of the bark. In this case the portions of tissue external to the inner corky layers or bands are thrown off as bork-scales (periderm of Weddell). This peculiar form of suberous tissue[1345] was first examined (not in cinchona) in 1845 by H. von Mohl, who called it rhytidoma (Borke of the Germans). In C. Calisaya it is of constant occurrence, but not so usually in C. succirubra and some others; the rhytidoma therefore affords a good means of distinguishing several barks.
The inner portion of the bark exhibits a middle or primary layer (mesophlœum),[1346] made up of parenchyme; and a second inner layer or liber (endophlœum)[1347] displaying a much more complicated structure. The primary layer disappears if rhytidoma is formed: barks in which this is the case are therefore at last exclusively composed of liber, of which Flat Calisaya Bark is a good example.
CONSPECTUS OF THE PRINCIPAL
SPECIES OF CINCHONA.
| SPECIES (EXCLUDING SUB-SPECIES AND VARIETIES) ACCORDING TO WEDDELL. | WHERE FIGURED. | NATIVE COUNTRY. | WHERE CULTIVATED. | PRODUCT. |
|---|---|---|---|---|
| I. Stirps Cinchonæ officinalis | ||||
| 1. Cinchona officinalis Hook | Bot. Mag. 5804 | Ecuador (Loxa) | India, Ceylon, Java. | Loxa or Crown Bark, Pale Bark. |
| 2. ” macrocalyx Pav. | Howard N. Q. | Peru | Ashy Crown Bark. The sub-species _C. Palton_ affords an important sort called _Palton Bark_ much used in the manufacture of quinine. | |
| 3. ” lucumæfolia Pav. | Do. | Ecuador, Peru. | ||
| 4. ” lanceolata R. et P.(?) | Do. | Peru | Carthagena Bark, confounded with Palton Bark, but is not so good. | |
| 5. ” lancifolia Mutis | Karsten tab. 11. 12. | New Granada | India | Columbian Bark. Imported in large quantities for manufacture of quinine.The soft Columbian Bark is produced by Howard’s var. _oblonga_. |
| 6. ” amygdalifolia Wedd. | Wedd. tab. 6. | Peru, Bolivia | A poor bark, but not now imported. | |
| II. Stirps Cinchonæ rugosæ | ||||
| 7. Cinchona pitayensis Wedd. | Karst. tab. 22. (C. Trianæ). | New Granada (Popayan) | India | Pitayo Bark. Very valuable; used by makers of quinine; it is the chief source of quinidine. |
| 8. ” rugosa Pav. | Howard N. Q. | Peru | Bark unknown, probably valueless. | |
| 9. ” Mutisii Lamb. | Do. | Ecuador | Bark not in commerce, contains only aricine. | |
| 10. ” hirsuta R. et P. | Wedd. tab. 21. | Peru | ||
| 11. ” carabayensis Wedd. | Wedd. tab. 19. | Peru, Bolivia | Bark not collected. | |
| 12. ” Pahudiana How. | Howard N. Q. | Peru | India, Java | A poor bark, yet of handsome appearance; propagation of tree discontinued. |
| 13. ” asperifolia Wedd. | Wedd. tab. 20. | Bolivia | Bark not collected. | |
| 14. ” umbellulifera Pav. | Howard N. Q. | Peru | Bark not known as a distinct sort. | |
| 15. ” glandulifera R. et P. | Do. | Peru | Do. | |
| 16. ” Humboldtiana Lamb. | Do. | Peru | False Loxa Bark, Jaen Bark. A very bad bark. | |
| III. Stirps Cinchonæ micranthæ | ||||
| 17. Cinchona australis Wedd. | Wedd. tab. 8. | South Bolivia | An inferior bark, mixed with Calisaya. | |
| 18. ” scrobiculata H. et B. | Do. | Peru | Bark formerly known as Red Cusco Bark or Santa Ana Bark. | |
| 19. ” peruviana How. | Howard N. Q. | Peru | ||
| 20. ” nitida R. et P. | Do. | Peru | India | Grey Bark, Huanuco or Lima Bark. Chiefly consumed on the Continent. |
| 21. ” micrantha R. et P. | Do. | Peru | India | |
| IV. Stirps Cinchonæ Calisayæ | ||||
| 22. Cinchona Calisaya Wedd. | Wedd. tab. 9. | Peru, Bolivia | India, Ceylon, Java, Jamaica, Mexico. | Calisaya Bark, Bolivian Bark, Yellow Bark. The tree exists under many varieties, bark also very variable. |
| 23. ” elliptica Wedd. | Do. | Peru (Carabaya) | Carabaya Bark. Bark scarcely now imported. C. sunsura Miq. (flower and fruit unknown) may perhaps be this species. | |
| V. Stirps Cinchonæ ovatæ | ||||
| 24. Cinchona purpurea R. et P. | Howard N. Q. | Peru (Huamalica) | Huamalies Bark. Not now Imported. | |
| 25. ” rufinervis Wedd. | Do. | Peru, Bolivia | Bark, a kind of light Calisaya. | |
| 26. ” succirubra Pav. | Do. | Ecuador | India, Ceylon, Java, Jamaica. | Red Bark. Largely cultivated in British India. |
| 27. ” ovata R. et P. | Do. | Peru, Bolivia | India(?), Java(?) | Inferior Brown and Grey Barks. |
| 28. ” cordifolia Mutis | Karsten tab. 8. | New Granada, Peru | Columbian Bark (in part). Tree exists under many varieties; bark of some used in manufacture of quinine. | |
| 29. ” tucujensis Karst. | Karsten tab. 9. | Venezuela | Maracaibo Bark. | |
| 30. ” pubescens Vahl | Wedd. tab. 16. | Ecuador, Peru, Bolivia | Arica Bark (Cusco Bark from var. Pelletieriana). Some of the varieties contain aricine. C. caloptera Miq. is probably a var. of this species. | |
| 31. ” purpurascens Wedd. | Wedd. tab. 18 | Bolivia | Bark unknown in commerce. | |
The liber is traversed by medullary rays, which in cinchona are mostly very obvious, and project more or less distinctly into the middle cortical tissue. The liber is separated by the medullary rays into wedges,[1348] which are constituted of a parenchymatous part and of yellow or orange fibres. The number, colour, shape, and size, but chiefly the arrangement of these fibres, confer a certain character common to all the barks of the group under consideration.
The liber-fibres[1349] are elongated and bluntly pointed at their ends, but never branched, mostly spindle-shaped, straight or slightly curved, and not exceeding in length 3 millimetres. They are consequently of a simpler structure than the analogous cells of most other officinal barks. They are about ¼ to ⅓ mm. thick, their transverse section exhibiting a quadrangular rather than a circular outline. Their walls are strongly thickened by numerous secondary deposits, the cavity being reduced to a narrow cleft, a structure which explains the brittleness of the fibres. The liber-fibres are either irregularly scattered in the liber-rays, or they form radial lines transversely intersected by narrow strips of parenchyme, or they are densely packed in short bundles. It is a peculiarity of cinchona barks that these bundles consist always of a few fibres (3 to 5 or 7), whereas in many other barks (as cinnamon) analogous bundles are made up of a large number of fibres. Barks provided with long bundles of the latter kind acquire therefrom a very fibrous fracture, whilst cinchona barks from their short and simple fibres exhibit a short fracture. It is rather granular in Calisaya bark, in which the fibres are almost isolated by parenchymatous tissue. In the bark of C. scrobiculata, a somewhat short fibrous fracture[1350] is due to the arrangement of the fibres in radial rows. In C. pubescens, the fibres are in short bundles and produce a rather woody fracture.
Besides the liber-fibres, there are some other cells contributing to the peculiarity of individual cinchona barks. This applies chiefly to the laticiferous ducts or vessels[1351] which are found in many sorts; they are scattered through the tissue intervening between the middle cortical layer and the liber, and consist of soft, elongated, unbranched cells, mostly exceeding in diameter the neighbouring parenchymatous cells.