PllEFACE. 
V 
have only for a short time occupied the atten- 
tion of observers, or which depend upon obscure and 
ill-understood evidence, are by no means so clearly 
defined as could be wished. To explain those prin- 
ciples, to adduce the evidence by which their truth 
is supposed to be proved, or the reasoning upon 
which they are based in cases where direct proof is 
unattainable ; to show the causes of errors that are 
now exploded, and the insufficiency of the arguments 
by which doubtful theories are still defended, — in 
fine, to draw a distinct line between what is certain 
and what is doubtful, — are some of the objects of this 
publication, which is intended for the use of those 
who, without being willing to occupy themselves 
with a detailed examination of the vast mass of evi- 
dence upon which the modern science of botany is 
founded, are, nevertheless, anxious to acquire a dis- 
tinct idea of the nature of that evidence. Another 
and not less important purpose has been to demon- 
strate, by a series of well-connected proofs, that in no 
department of natural history are the simplicity and 
harmony that pervade the universe more strikingly 
manifest than in the vegetable kingdom, where the 
most varied forms aie produced by the combination 
of a very small number of distinct organs, and the 
most important phenomena are distinctly explained 
by a few simple laws of life and structure. 
In the execution of these objects, I have followed 
very nearly tlie method recommended by the cele- 
brated Professor De Candolle, than whom no man is 
entitled to more deference, whether you consider the 
soundness of his judgment in all that relates to order 
and arrangement, or the great experience which a 
long and most successful career of public instruction 
has necessarily given him. 
A 4 
