ORIGINAL AND EXTRACTED ARTICLES. 
ON THE ANATOMY OF DKUGS. 
BY HENRY B. BRADY, F.L.S., ETC. 
{Concluded from p. 4G3.) 
Dicotyledons. —Exogenous or Dicotyledonous plants form the chief portion 
of the vegetation of every latitude, and as they yield by far the largest number 
of the elements of our vegetable Materia Medica, anything like a general sketch 
of the structure of their various medicinal products, even in outline, would far 
exceed the limits assigned to us. Neither is there much necessity for an 
elaborate or extended survey of them. With a higher organization we have, it 
is' true, a larger margin for variation in minute particulars ; but the existence 
of slight peculiarities can scarcely be said to increase the difficulties of the 
student, inasmuch as there is generally an obvious and easily-read relation of 
all the parts to a common typical plan of structure. 
Thus, when the characters of any common Exogenous stem are understood, a 
section of quassia, sassafras, guaiacum, or logwood will need no ej^planation, 
for though each will be found to differ from the others in certain respects, it 
will be readily seen that the differences are dependent on the degree of develop- 
ment of the parts, and not on the presence of any superadded structure nor 
even on any alteration in the general arrangement of the organs forming the 
stem. The transverse section of these or any similar stem shows the wmod, 
arranged in rings, each of which corresponds to a year’s growth—a central 
pith or an indication of the position the pith had occupied in the earlier stages 
—and an external bark. Radiating lines (“medullary rays”) traverse the 
wood connecting the central cellular tissue (pith) with the external cellular 
portion (bark). A longitudinal section through the centre of the stem is but 
a profile view of the organs just enumerated, but as the medullary rays are 
never quite straight or uniform in their growth, only patches of them are seen 
here and there, taking the appearance of a flat, regular, network of elongated 
cells. A third section cut longitudinally, but not through the centre of the 
stem (tangential), will cross the medullary rays, showing their thickness and 
further indicating their cellular nature. Of course in the chips of any of these 
woods as found in commerce only portions of these structures are to be found, 
as both bark and pith are usually rejected. In many woods, guaiacum for ex¬ 
ample, the inner layers become uuich hardened by secondary deposit, acquiring 
thereby a darker colour. The general appearance of the wood under the 
microscope is not altered thereby, except when viewed with high magnifying 
powers, which show, especially in transverse sections, the filling of the cells in 
the manner alluded to. 
From woods, we may pass to the consideration of the cellular tissues which en¬ 
velop them and in no section of the vegetable Materia Medica has the use of the 
microscope been more extensive than in the examination of the various products 
of Cinchona and allied genera known under the general name of “Peruvian 
barks,” and few subjects are so beset with sources of error and confusion. To 
obtain authentic specimens of many varieties is a matter of extreme difficulty, 
and, until recently, that of ascertaining their precise botanical and geographical 
origin was scarcely less. The works of Weddell, Delondre, Phoebus, and others, 
and the beautiful monograph of Mr. J. E. Ho\vard, have of late years cleared 
up many botanical doubts, and the explorations of Mr. Spruce in the cinchona 
countries, have, in like manner, throw'n much light on the distribution of the 
various species. Hence, any writer in the present day wdio cannot command the 
