PREFACE. Vll 



views of several of the first botanists of the day, who have been in the 

 habit of considering each species with reference to the forms it may 

 assume over the whole extent of its area. There is no doubt that in 

 the case of a large number of common and widely-spread plants, such 

 as the Water Crowfoots, the Briar Hoses, the Brambles, Hawkweeds, 

 Willows, etc., there are numerous races of greater or less permanency, 

 which are more or less positively distinct, and well worthy of being 

 studied as such by those who have leisure and patience to devote them- 

 selves to the subject, and which should by no means be neglected by 

 the botanist who would be thoroughly grounded in his knowledge of 

 plants ; yet it is believed, that with the general advance of science, the 

 conviction is gradually spreading that the raising these races to the 

 rank of species is giving them an undue importance, and that it is at 

 once more philosophical and more practically convenient, as well to the 

 general botanist in the higher branches of the science as to the more 

 superficial amateur, to retain for the meaning of a species the limits 

 affixed by the original principles of Linnaeus. The only change which 

 the Author has made in this respect in the present edition is the ad- 

 mission as species of the Ivy Ranunculus (i£. liederaceus) and the green 

 Spleenwort {Asplenium viride), in which cases his own opinions may 

 not be sufficiently established to interfere with the authority of general 

 custom, and of the intermediate Bladderwort {Utricularia media), on 

 the authority of Irish botanists, the Author himself being very imper- 

 fectly acquainted with the plant. With regard to the charge of having 

 based his views upon the study of herbarium specimens alone, the Au- 

 thor can only reply that this is a mistake, and repeat from his former 

 Preface that his generalizations are chiefly "founded on personal ob- 

 servation of living plants, made during many years' residence on the 

 Continent as well as in this country, and on repeated comparison of 

 specimens collected from the most varied and distant points of the 

 geographical areas of the several species." 



Four species have been added in the present edition : the Claytonia, 

 introduced from America, but now generally established as a weed of 



