xviii INTRODUCTION. 
given, that all the European portion of the genus must 
be huddled together under one specific title; a measure, 
the absurdity of which is sufficiently obvious, because 
to adopt it would be only disputing about terms, since 
it would then be necessary to distinguish certain modi- 
fications ; and it is immaterial whether these be termed 
species or varieties. For why do we distinguish species 
among genera? except as the means of giving precision 
to our ideas, and consequently correctness to our lan- 
guage; by indicating certain modifications of structure 
considered to be of inferior importance to those which 
distinguish genera, and whose supposed limits are de- 
fined by what is called a specific character. By species 
then I wish to be understood here to mean, an assem- 
blage of individuals, differing in particular respects 
from the rest of the genus, but having more points of 
affinity among themselves than with others; their 
union being therefore natural. 
But if, as I have attempted to abel there are no 
limits to the species, it is impossible to give them ri- 
gorous definitions ; and with a firm conviction of the 
truth of this, have I set about a revision of the genus. 
Upon these principles I have proceeded throughout. 
On commencing an examination of the causes 
-whence so much confusion has arisen, I was presently 
assured that no inconsiderable part of the difficulty 
might be removed by ceasing to insist on the trifling 
distinctions upon which a number of botanists have 
recently established their species. For it is evident 
that where only a few tolerably tangible characters are 
to be obtained, no course is so certain to destroy their 
importance as that of frittering them away till they 
become confounded with one another, Nor is it suffi- 
