354 



RUBIACEiE. 



taugentially extended cells of the middle cortical layer and the 

 medullary rays. In percentage of alkaloids^ Cartliagena 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. 



mtay 



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^cinaUs 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.^ 



Microscopic Structure— The first examination of the^ minute 

 structure of Cinchona barks is due to Weddell, whoso 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 ot 

 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. Tne 

 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 

 G. Calisaya, it separates easily, at least in the older bark, whereas m 

 others as C. succirubra, the bark even of trunks Is always coated witQ 

 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 

 th 



th 



e portions of tissue external to the inner corky layers or bands are 

 rown off as hork-scalcs (peridei-ni of Weddell). This peculiar form oi 



suberous tissue* was first examined {not in cinchona) in 1845 by H. v 

 Mohl, who called it rhytidoma {Borke of the (Germans). In C. CahsaiP 

 it IS of constant occurrence, but not so usually in C. succirubra ami 

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

 guishing several barks. 



middle 



(mesophlceum),' made up of parenchyme : and a second inner layer or 

 l^er (endophloeumy displaying a much more complicated structone- 



vlJ^^^^^ ^^ ^° Indian village eastward of 



P^Ff^^'"', ?f^ '"^P °f *lie country btw cen 

 Pasto and BogotA in Blue Book (Eastlmlla 

 Chmchona Plant) 18G6. 2',7. ^ 



hil V"? ^"^""'^^ included by Weddell in 



opinion belonging to the genus. .. 

 » Hist. nat. iUh Quinqi'inax, *?■"•"•„ gi. 

 * FlCickiger, Grundhgen, Berlin, 1»/^- 



^y- *8. 11 ,?,!>-p of 



'Envelopp>' ou ttimiue """''^''^ 

 Weddell ; Mlffelrinde of the Germans 



« In German Bast, or Phloem of niort-- 

 nermin botany. 



