ANATOMICAL STRUCTURE. 37 
and often approximately closed circle. In cases where they remain 
small, they may be easily overlooked when the sections are softened 
with potassa instead of the less destructive alkali ammonia. 
According to Karsten the lacticiferous ducts occur in the 
youngest branches of all or nearly all Cinchonas and their nearest 
allies, but in individual species they remain very narrow and soon 
become quite insignificant ; a change which is also in part thereby 
effected, that in their interior a new formation of parenchymatous 
cells takes place.* 
Although these lacticiferous ducts can scarcely be considered as a 
peculiarity of individual Cinchonas, they are, indeed, wanting in some 
commercial barks, and are retained in a state of preservation in 
others, in so far as the entire outer bark has not become complete- 
ly destroyed by the formation of bork. 
The lacticiferous ducts may, moreover, according to Weddell,’ 
be best traced in the medulla of living branches, especially near 
the nodes of young axes. 
More important points of discrimination are afforded by the bast 
of the Cinchona barks (Plate VII, B. C. v), which, in consequence 
of the removal of the bork, represents exclusively some varieties 
of commercial bark (Plate VII, B). It is intersected by medullary 
rays (Plate VII, v), which radiate from the wood in 3, or at most 4 
parallel rows (large medullary rays, chief medullary rays), The 
cells of the medullary rays are almost invariably larger than those 
of the bast parenchyma, and increase toward the exterior in width 
as also in the number of the individual rows. In the tissue of the 
medullary rays, especially in the outermost layers, isolated cells 
often become thickened to stone-cells (Plate VII, C); still more 
frequently many contain a crystalline powder, and also without 
becoming lignified. Sosa : 
The bast contains as its most prominent constituent spindle- 
shaped fibres (Plate VII, sc), which are extended in the direction 
of the axis, and whose walls become thickened at a very early 
period. When the cells become thickened to a less extent, and do 
not terminate in a point, they are distinguished as staf-ced/s, or 
staff-shaped stone-cells. | 
In the younger barks of most species the bast-fibres are found 
sparingly scattered, but with increased age they multiply consider- 
ably in number, lose their cavity almost completely, and press back 
_ the surrounding bast-parenchyma quite strongly. On a transverse 
1 ee Vogl, Chinarinden des ‘Wiener Grosshandels, p. ia: De Bary, Anatomie, 
Pp. 558. : : o 3 
2 Hist, nat. des Quinguinas, Tab. I. Fig. 26. 
