394 Professor Henslow's Catalogue of British Plants. 



consideration, or the degree in which the species may have claim to 

 he held indigenous to Britain, are fourfold, and are indicated hy 

 particular marks, namely, species " possibly introduced by the agency 

 of man"f — " Naturalized species, certainly not indigenous"* — oc- 

 casionally found wild, but not even naturalized, extinct, or erroneously 

 introduced, and which ought to be excluded from our Floras" (o) ; — 

 admitted natives. The species included in the Flora Cantabrigiensis 

 are distinguished by the addition of a letter (c,) and the goodness 

 of their titles to be considered natives of the district, to which this 

 Flora relates, is also indicated. 



On the very debateable question touching the identity or distinct- 

 ness of species, it is in vain to expect uniformity of judgment, while 

 mere opinion, in contradistinction to fixed rules, is the only guide for 

 our decisions. No fixed rules have yet been discovered or admitted, 

 and we might add, probably with equal truth, that no fixed rules 

 ever will be discovered. The subdivisions of genera, or (what is 

 the same thing,) the union of varieties into species, must rest on the 

 ground of expediency, so long as absolute rules are wanting; and, 

 viewing the question in this light, we unhesitatingly recommend the 

 catalogue of Professor Henslow as the best guide for the botanist of 

 Britain ; agreeing with the Professor's suggestions in most instances, 

 though inclined to sink the majority of his questionable species into 

 the grade of mere varieties. We do not, however, so fully agree 

 with the manner of classifying the species not indigenous or not 

 found at all in Britain. It appears a more judicious course to join 

 the species " occasionally found wild," with the " naturalized spe- 

 cies," both classes being " certainly not indigenous ;" and the differ- 

 ence between them being one of degree only, where the degrees are 

 so very difficult to distinguish, that no uniformity of opinion can be 

 hoped for. The classes of extinct and mistaken species are readily 

 separable from the preceding, since these species are not found wild 

 in any sense of the term. They are, indeed, equally different from 

 each other, yet cannot be completely separated ; it being now quite 

 impossible to decide whether several of the species, the names of 

 which are still included in our Floras, have become extinct ; or whe- 

 ther such names were introduced originally through some mistake 

 about the plants to which they were applied. It would be well to 

 expunge from our descriptive Floras the names of all species not now 

 found wild. The remainder would unite into two classes, — the tvild, 

 but certainly introduced ; — the established, of uncertain origin. The 

 subdivisions of these two groups would be merely those of degree. 

 In the former, the extent to which the species have become natu- 



