PREFACE. 
vii 
opinions, whether admitted as true or rejected as 
erroneous, should be given at length. 
In the first edition, this department was not so 
complete as I could have wished ; in the present, I 
have been enabled, chiefly by the aid of Professor 
De Candolle's Physiologie, to extend, and, as I hope, 
to improve it very materially. 
Next followed in the first edition Taxonomy : or 
some account of the Principles of Classification ; — 
a very important subject, comprehending not only 
a view of the various methods of arrangement em- 
ployed by botanists in their systematic works, but an 
explanation of the principles by which the limits of 
genera and species are determined. It also shews 
the mode of obtaining a correct view of vegetation, 
of conducting the examination of unknown plants 
with precision, of avoiding errors in consequence of 
accidental aberrations from ordinary structure, and 
of forming a just estimate of the mutual relation 
that one part of the vegetable kingdom bears to 
another. 
But in the present edition I have entirely omitted 
this book : firstly, because of the great additions that 
have been made to other topics ; and, secondly, be- 
cause it is extensive enough to form a work by itself- 
The whole of what was contained in this part of the 
first edition will be found incorporated with the pre- 
fatory matter of the second edition of the Introduction 
to the Natural System of Botany, now in preparation. 
After this, I have taken Glossology (Book III.) ; 
or, as it was formerly called. Terminology ; restrict- 
ing it absolutely to the definition of the adjective 
terms, which are either used exclusively in Botany, 
or which are employed in that science in some parti- 
cular and unusual sense. The key to this book, and 
