Ifxttatt. 



In attempting to describe the chsiracters of the various 

 species of Hiebacittm which are natives of the British Islands, 

 I am fully conscious of the intricacy of the subject, and of 

 the great difficulty which exists in distinguishing between true 

 species, and varieties or extreme forms. When varying altitude, 

 exposure, geological formations, soil, and meisture, all modify 

 the aspect of the same plant, and not unfrequently to so great 

 a degree, as to leave scarcely a trace of resemblance in the 

 extreme forms, to the eye of a casual observerj^ it wiU be seen that 

 a difficulty exists, with regard to this genus, which attaches 

 comparatively to few genera, and which patient investigation, 

 and careful comparison can alone surmount. 



It was under the impression that, as far as the plants of 

 Britain are concerned, this genus had received a smaller share of 

 accurate and diligent investigation than almost any other, (owing 

 mainly no doubt to want of opportunity,) Ijhat, in conjunction with 



