viii PREFACE. 



Bentham's and my Genera Plantarum. I have also made changes in the limits 

 of the Species of certain Genera, and of their subordinate forms, in which 

 matter I have often had regard to suggestions and materials laid before me 

 by Mr. Baker (who has again revised the sheets as they passed through 

 the press), and Mr. Nicholson ; and for the first forty-one Orders to notes 

 made for me by Mr. Ball, F.R.S. These last have a special value, due to 

 Mr. Ball's critical knowledge of so many European Floras, and his excel- 

 lent judgment. I have further profited by the last edition (8th) of Pro- 

 fessor Babington's accurate and critical Manual, and have collated the 

 whole with the second edition of Ny man's Sylloge Floras Europcece, and of 

 Newbould's and Baker's edition of Watson's Cybele. To Mr. Arthur 

 Bennett, F.L.S., of Croydon, I am indebted for revising the Genus 

 Potamogeton, and for notes upon Carices. 



The collation of the British Flora with Nyman's Sylloge has not been 

 satisfactory throughout, because of the wide divergence of the views there 

 upheld regarding the Species of such Genera as Rubus, Rosa, &c. , from 

 those held by English botanists. This is doubtless due to the fact that 

 characters which are constant and strong in one country beeome vague 

 and even evanescent in others ; insomuch that I am led from examination 

 and study to believe that, in respect of the subdivision of the European forms 

 of such Genera into Species, Sub-species, and Varieties, the materials in 

 Britain may give one result, those in France another, in Scandinavia a 

 third, and in Germany a fourth. 



I am disposed to think that the term Sub-species (which represents a 

 stage of evolution between Species and Variety) should be given to many 

 forms considered by some as Species and as Varieties by others ; and that 

 this would facilitate the better understanding especially of the larger 

 critical Genera. The various forms of fruticose RuU, for example, whether 

 all treated as Species, or all as Varieties, present to me a mere chaos ; 

 whereas, when treated as Sub-species and Varieties, however imperfectly, 

 they fall into comprehensible groups, whose cross affinities may thus be 

 more clearly enunciated. 



Lastly, I have ventured to introduce into this Edition, under the de- 

 scription of the flowers of various Genera, characters concerned in the process 



