X PREFACE. 



particularise. We have inserted a few well-authenticated 

 additional localities, but have not attempted any general 

 revision of this part of the work. 



In the case of Hieracium, the number of species recognized 

 in this country has so greatly increased during the last 

 twenty years, that it has been thought desirable to substi- 

 tute an entirely fresh account of the genus, and this has 

 been drawn up by Miss Rachel P. Thompson, under the 

 guidance of Mr. F. J. Hanbury, and forms a very valuable 

 addition to the book. 



In the somewhat similar case of Rulus, Professor 

 Babington having for so many years been the recognized 

 authority on the genus in this country, it \\ as felt that it 

 would not be fitting for his account to be removed from 

 the book, although it was clear that he had intended to 

 rewrite it. It was therefore arranged by the kind per- 

 mission of the Rev. W. Moyle Rogers to reprint, as an 

 appendix, a conspectus of the groups and species, from 

 that gentleman's admirable ' Handbook of British Ruli? 



During the past twenty years great changes have taken 

 place in the matter of nomenclature. The publication of 

 the * Index Kewensis ' and other lesser works bearing on 

 the subject, besides greatly facilitating the study of 

 botanical literature, has demonstrated how imperfectly 

 the laws of priority as regards names have been observed 

 in the past. It is only by a strict observance of these 

 laws that any approach to finality is likely to be reached, 

 and we have therefore adopted the earliest names as far 

 as we have been able to ascertain them, taking 1753 as 

 the starting-point for both genera and species. In doing 

 this we have had to make a large number of alterations 

 in names and authorities. 



It has only been possible for us to carry out this work 

 by the kindness of the many friends and correspondents, 



