XXVI 



INTRODUCTION. 



resemble one another yet more closely in the 

 essential characters of fructification. A species 

 (kind) is an assemblage of individual plants, agree- 

 ing with each other in all essential points ; and 

 individuals which difi'er one from another in minor 

 points, such as an irregular formation of leaves 

 or mode of growth, unusual colour of flowers, ex- 

 traordinary number of petals, &c., are termed 

 varieties. These words are frequently used 

 loosely in common conversation; but the habit 

 cannot be too carefully avoided in botanical de- 

 scriptions, as calculated to produce endless con- 

 fusion. Throughout these pages they will be 

 employed exclusively with the meanings above 

 assigned, which will be rendered clearer by the 

 following examples : — The wild, sw^eet-scented 

 violet is called by botanists Viola odorata ; the 

 former name, Viola, indicating that it belongs to 

 the genus so called, and being therefore termed 

 its generic name. Besides the scented violet, we 

 have in England the dog-violet, the marsh-violet, 

 the pansy, and several others, all belonging to 

 the same genus, and being therefore included 

 under the name Viola : but the dog-violet differs 

 from the sweet-scented, in having acute sepals 

 and leafy stems, .w^hereas the latter has blunt 

 sepals, and the leaves spring directly from the 

 roots. The dog-violet is therefore a distinct spe- 

 cies, Viola canma. The marsh-violet and pansy 

 differ also in important characters ; they are 

 therefore also considered distinct species, the fact 

 being indicated by the addition of the specific 

 or trivial names, palustris and tricolor, to the 

 generic name Viola, The flowers of the scented 

 violet are sometimes white and sometimes blue ; 



