ANATOMICAL STRUCTURE. 85 
acquire their peculiar tint. The light grayish-yellow or yellowish-red 
bark of C. micrantha begins to assume a blood-red color imme- 
diately after its separation; the white bark of C. australis changes 
to a rust color, as soon as the external layer which has been beaten 
softis removed. In C. Calisaya the fresh bark is externally of a light 
greenish-yellow color; in C. pubescens, of a dirty white or green. 
These colors are indeed subject to some final variation, accord- 
ing to whether the drying of the bark is effected more or less quickly 
by a fire, or by allowing it to remain exposed to the air and sun, 
whereby, frequently through rain and dew, the barks again become 
moist. The remarkable change of color of the fresh bark always 
remains a noteworthy characteristic of the true Cinchonas. 
In the color of the bark a serviceable means is presented for the 
characterization of the barks individually, or at least for forming 
the varieties into groups. The older investigators of this subject, 
as also the bark collectors themselves, have, therefore, not improp- 
erly referred to these distinctions as: Quina amarilla (yellow), 
blanca (white), colorada or roza (red), naranjada (orange), negrilla 
(brown), etc. The plates of the works mentioned under numbers 
2, 6 and 37 in section XVIII give a very good representation of 
the colors of most Cinchona barks. 
The Cinchona barks in their structure do not display any more 
remarkable peculiarities than many other barks; and that which 
imparts to them particular features may be comprised in the follow- 
ing statements, 
The formation of cork (feriderm) takes place in the primary 
bark in the zone of tissue located nearest to the inner surface of 
the epidermis. The cork cells of the barks of the true Cinchonas 
which occur in commerce are thin-walled, and show the usual tabu- 
lar form and radial arrangement (Plate VII, A.C.e). The younger 
barks are usually still covered with cork, but in older ones this is 
not always the case. Even the older barks of Cinchona succirub- 
ra, for example, still occur in commerce with the cork adhering, 
while the equally strong stem-barks of C. Calisaya yield to the 
formation of bork and do not present the uninjured cork, which, in 
consequence of the formation of corky bands in the inner tissue, 
is thrown off together with the outer bark. The cascarilleros ap- 
propriately designate the shallow trough-shaped bork cavities 
which are thus formed as Conchas, on account of their resemblance to 
flat mussels. Where they are longitudinally extended and also pos- 
sibly coalesce, they present an appearance as though having been 
formed by impressions of the fingers. These conchas are present 
to the most striking extent in the stem-barks of C. Calisaya. 
