354 RUBIACE^. 



tangentially extended cells of the middle cortical layer and the 

 medullary rays. In percentage of alkaloids, Carthagena barks are 

 liable to great variation. 



The Pitayo Barks are restricted to the south-western districts of 

 Columbia/ 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 jyikiyensis 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. offi,cinalis or C. succiruhra. 



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.^ 



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.^ 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. succiruhra, 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* 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. succiruhra and 

 some others ; the rhytidoma therefore affords a good means of distin- 

 guishing several barks. 



The inner portion of the bark exhibits a middle or primary layer 

 {mesophloeum),^ made up of parenchyme ; and a second inner layer or 

 liber (endophloeumy displaying a much more complicated structure. 

 The primary layer disappears if rhytidoma is formed : barks in which 



^ Pitayo is an Indian village eastward of opinion belonging to the genus. 



Popayan; see map of the country btween ^ Hist. nat. des Quinquinas, tab. ii. 



Paste and Bogota in Blue Book (East India * Fluokiger, Grundlagen, Berlin, 1872. Gl. 



Chinchona Plant) 1866. 257. fig. 48. 



2 Two species included by Weddell in " Enveloppe oil tunique . cellulaire of 



his Notes sur les Quinquinas, namely C. Weddell ; Mittelrinde of the Germans. 



Ckomeliana Wedd. and C. harbacoen»is * In German Bast, or Phloem of modern 



Karst., have been omitted, as not in our Gennan botany. 



