al PREFACE. 
any real difference of opinion as to the richness and diversity 
of our vegetable productions, but is occasioned by a different 
appreciation of the value of the species themselves. The 
Author has long been persuaded that the views originally enter- 
tained by Linnzeus of what really constitutes a species, were 
far more correct than the more limited sense to which many 
modern botanists seem inclined to restrict the term ; and that 
in most cases where that great master had good means of obser- 
vation, he succeeded admirably in the practical application of 
his principles. At any rate, if those minute distinctions by 
which the innumerable varieties of Brambles, of Roses, of 
Hawkweeds, or of Willows have of late years been characterized, 
are really more constant and more important than the Author’s 
experience has led him to conclude, they cannot be understood 
without a more complete acquaintance with trifling, vague, and 
sometimes theoretical characters, than he has himself been able 
to attain, or than can ever be expected from the mere amateur. 
It is considered, therefore, that such details would be out of 
place in the present work, and those who feel sufficient interest 
in the subject to devote their leisure hours to the investigation, 
can only hope to master it by a close and patient study of the 
numerous, often very carefully elaborated monographs published 
‘in Germany, Sweden, and France, as well as in this country. 
The species are here limited according to what are conceived to 
have been the original principles of Linneus, and the Author, 
in submitting his views to the judgment of the scientific world, 
trusts thet they will not be attributed to hasty generalizations 
or conjectural theories, but that they will be generally recog- 
nized as founded on personal observation of living plants, made 
during many years’ residence on the Continent as well as in 
Rumex, Salix, Juncus, Potamogeton, Carex, genera the limits of whose 
species are notorious subjects of controversy ; leaving 300 to be accounted 
for by the inclusion of doubtful and introduced species, and by a subdivision 
of the species of various small genera.—J. D. H. 
