INTRODUCTION. 
vii 
can scarcely be available, except to persons who are 
partially acquainted with the plant under examination, 
or with some of its near allies. Between these extremes 
a middle course was steered, by giving diagnostic re- 
marks where, and where only, they appeared necessary 
for the discrimination of British species, or such very 
distinct foreign ones as might possibly be found in this 
country, and be confounded with them. In the sixth, 
seventh, and also in the present edition these rules have 
been slightly departed from. So many species have 
been, of late years, introduced from the Continent with 
seed-corn, or have escaped from our gardens, and so 
many of our former well-known species have been sepa- 
rated into two or more, that it has been deemed proper 
to extend, in several instances, the characters of both 
the genera and species, introducing frequently a notict 
of the more minute parts which a practised botanist 
requires to examine, but which a student may omit, it 
his object be merely to attain a knowledge of the name, 
until he has advanced in the study. Rarely, however, 
have the genera or species been made to depend on such 
minute characters, and therefore few alterations have 
been proposed in the limits of either one or other from 
what will be found in former editions : when such alter- 
ation has taken place in the former, it is solely from, a 
desire of simplifying the generic characters. 
What is a genus, or what is a species, is a point upon 
which scarcely two botanists are quite agreed at the pre- 
sent day. With regard to the former, however much it 
may be necessary to subdivide in a system comprehending 
the known plants of the whole world, so as to retain only 
a limited number of species in each genus, the same does 
not apply to a local Flora ; and it is there preferable to 
constitute sections or subgenera, particularly when the 
limiting characters are inconstant, difficult, or obscure. 
A species, in the Linmean sense of the word, cannot be 
A 4 
