xiv 
INTRODUCTION. 
not being the result of sexual contact : this group correspondt. 
with the Cryptogamia of Linnaeus. 
Such is the foundation upon which the natural system of 
Jussieu is arranged; his classes amount to fifteen, eleven of 
which are included in the Dicotyledoneous plants ; three in the 
Monocotyledoneous ; and one in the Acotyledones : these 
classes are not distinguished by any particular names — each 
class is again subdivided into natural orders, but the system 
has undergone so many revisions, and the labours of living 
botanists are so constantly extending or diminishing the num- 
ber of these orders, that it is not very easy to ascertain their 
precise number ; according to Sir J. Smith, (see his Grammar 
of Botany) they only amount to one hundred, v.hile other 
botanists enumerate nearly double that number. Each order is 
defined by tolerably full definitions, taken, first from the parts 
of fructification, and secondly from secondary characters, 
founded on other circutnstances. 
Having thus given an analysis of the two great systems 
by which botanists of the present day are divided, and to 
which reference is made in the Flora Medkja, the limits 
of our undertaking will only admit of our saying a few words 
on the subject of vegetable secretions, a subject which above 
all others should interest the Medical Botanist. It is from 
those secretions that he is to draw his medicinal store, and on 
them that he is to exercise his chemical and pharmaceutical 
art; while as a subject worthy the attention of a philosophic 
mind, we know of none more curious than this part of vegetable 
physiology. The first thing that strikes us is the variety of 
secretions of different plants, or families of plants, by which 
they are distinguished from each other, and differing so mate- 
rially in smell, taste, sensible qualities, and medical virtues : 
even in the same plant, we frequently find a variety of secre- 
tions totally different; of this the peach tree offers a familiar 
example ; the gum of the tree being mild and mucilaginous, and 
agreeing very nearly, when in its purest state, with the gum of 
the Mimosa Nilotica, while the bark, leaves, and flowers abound 
with a bitter secretion of a dangerous quality ; the fruit again 
is replete with acid, mucilage, and sugar, and its own peculiar 
aromatic and volatile secretion, while in the kernel of the same 
fruit is contained a large portion of the Prussic Acid, which in 
its highest state of concentration is so noxious to animal life. 
