viii 
PREFACE. 
also to the substantive terms explained in Organo- 
graphy, will be found in a copious index at the end of 
the volume. 
These topics exhaust the science considered only 
with reference to first principles ; there are, however, 
a few others which it has been thought advisable to 
append, on account of their practical value. These 
are, firstly, Phytography (Book IV.); or, an ex- 
position of the rules to be observed in describing and 
naming plants. As the great object of descriptions 
in natural history, is to enable every person to recog- 
nise a known species, after its station has been dis- 
covered by classification, and also to put those who 
have not had the opportunity of examining a plant 
themselves into possession of all the facts necessary 
to acquire a just notion of its structure and affinities ; 
it is indispensable that the principles of making 
descriptions should be clearly understood, both to 
prevent their being too general to answer the intended 
purpose, or more prolix than is really requisite. It 
is the want of a knowledge of these rules that renders 
the short descriptions of the classical writers of an- 
tiquity, and the longer ones of many a modern tra- 
veller, equally vague and unintelligible. In this 
place are inserted a few notes upon the formation of 
an herbarium. 
After this, has been introduced (Book V.) a sum- 
mary of the little which is known of the laws that 
regulate the distribution of plants upon the surface of 
the earth ; a question which, however indefinite and 
unsatisfactory our information may at present be, has 
begun to assume such an appearance as to justify the 
expectation, that fiiture discoveries will explain the 
causes of the characters of vegetation being deter- 
mined, as they surely are, by cUmate. 
