266 royle's manual or materia medica, etc. 
with, espect to Belladonna, when he stated that the delete- 
rious principle of this plant is "a bitter and nauseous matter, 
soluble in spirits of iviiie, forming with tannin an insoluble 
combination, and furnishing ammonia from its decomposi- 
tion by fire/' 
Another striking illustration of the position, that the ad- 
vance of chemical discovery has still further confirmed the 
propriety and advantage of grouping vegetable substances, 
in accordance with a botanical arrangement, is derived 
from the Rosacea?. This order, according to Jussieu, was 
an extended one. If the whole order be taken, some di- 
versity of formation and products will be apparent; but it 
admits of subdivision in which exact analogy is maintained. 
In addition to the lines which botanical investigation has 
drawn around these subdivisions, chemical investigation 
has determined the source and principle of the activity of 
the individual species belonging to them to be one and the 
same. Thus taking Rosacea as the order, Ave find the 
^mygdaleae characterized, in connexion with structural re- 
semblance, by the presence of arnygdalin, which under 
proper circumstances yields an oil and prussic acid ; the 
Spiraeac containing an emetic principle, the Dryadeas and 
Roseau containing tannin, and lastly the Pomciceae contain- 
ing phlorndzin. 
We may find proof of the advantage and beauty of this 
mode of studying Materia Medica, in every order of the Jus- 
sieuan system, evincing that philosophy may be main- 
tained even in the apparently disjointed and promiscuous 
materials of this department, and that nature, true to herself, 
alone affords the clue to its detection. To search for 
properties in one class which belong to another, would 
be just as rational as to expect " grapes from thorns or figs 
from thistles." But we must return from this digression to 
the work before us. 
The primary division into plants is into two classes, Co- 
tyledonoxis and dicotyledonous. The first is divided into 
