PREFACE. 
plants referable to different families will not graft on each other, apparently, because the juices 
elaborated in different families of plants, though growing side by side, in the same soil, are so 
different in their- qualities that those of the one are unfit to nourish a branch taken from the 
other: while on the other hand two plants of the same natural family, however much the soils 
in which they respectively grow may differ, can generally, be readily grafted on each other. F rom 
the same cause, the action, namely, of organization on secretion, we find in a great many in- 
stances identical properties common to whole families of plants. Acrimony predominates 
throughout the Ranunculaceae and Cruciferae: narcotism is the characteristic of Papavera- 
ceae and Solanaceae: Apocyneae are generally poisonous and some of the species most viru- 
lently so: astringency is common to nearly all the arboreous Mimoseae as well as to many of the 
Caesalpineae, it equally predominates in Terminaliae, and the whole of the genus Quercus is 
: pre-eminently marked by that property. The Cucurbitaceae, Convolvulaceae and Euphor- 
biaceae are equally distinguished by properties the very reverse, the action of many species of 
each of these orders being violently drastic. The fruit of Rosaceae and seed of Leguminosae 
on the contrary, are so universally wholesome that it may be laid down as a general rule almost 
without exceptions, that they may be safely partaken of whenever they are met with. 
These few examples will suffice to show how vastly the study of properties is facilitated by 
an acquaintance with natural affinities, and will, I trust, at the same time serve to remove an 
objection which I have more than once hard urged against this work, that it did not sufficiently 
treat of Medical Botany. This objection could only be raised by those who did not sufficiently 
consider that its object was to establish principles on a scientific basis, as being the true way to 
attain the object sought for. There is no royal road to science, and until the medical man 
studies the principles of Botany as a science, he need never expect through an inspection of 
plates or specimens of medical plants to become a medical Botanist. But with only an elementary 
knowledge of Botany, such for example as a perfect knowledge of the structure of the flo wer and 
fruit, an acquisition not generally of very difficult attainment, the case is widely altered, since any 
that namely of making out the genus. But even without going so far 
the order of aplant, we are in possession of a fund of information, since, but little further trouble 
1s required to make ourselves acquainted with all that is yet recorded respecting that order, and to 
to science. The natural 
the pro- 
