Mr. Colebrooke on j^rrangements in Natural History. 43 



Art. IV. On Dichotomoiis and Quinary Arrangements in 

 Natural History. By Henrv Thomas Colebrooke, 

 Esq., F.n.S., F.L.S., F.G.S., 3fc. 



The distribution of natural objects into classes or orders, has been 

 compared to a geographical chart. " Natural orders," says Linnaeus, 

 " are related to each other by so many points, that they rather resemble 

 a geographical map than a continued series." It has, however, been 

 remarked, that the comparison is not correct. The affinities of an object 

 ramify in every direction, and cannot be well represented on a plane 

 surface. 



There is indeed a mode of classification, which has been aptly termed 

 dichotomous; and which might well be represented superficially. It 

 proceeds upon a selection of single characters, in succession; which, 

 taken affirmatively and negatively, furnish at each step two distinctions: 

 one for objects possessing the character in question; the other for such as 

 want it. For example, at the very first step, organic and unorganic sub- 

 stances; and, thereafter, vertebrate and non-vertebrate animals. So 

 cotyledonous and acotyledonous vegetables ; and again, monocotyledonous 

 and dicotyledonous plants. If the series, in which characters are seve- 

 rally noticed, be judiciously chosen, the dichotomous arrangement, well 

 pursued, supplies a very instructive key to natural knowledge. Many 

 professedly natural distributions have been so ordered. 



But a more instructive arrangement is that, which exhibits an object in 

 all its bearings ; which places it amidst its cognates ; and contiguous to 

 them again, those which approach next in degree of affinity; and thence 

 branching every way to remoter relations. 



If we imagine samples of every natural object, or a very large group 

 of them, to be so marshalled, we must conceive such a group as occupy- 

 ing, not a plane, but a space of three dimensions. Were it immensely 

 numerous, the space so occupied would approximate to a globular form: 

 for indefinite space, around a given point, is to the imagination sphe- 

 roidal, as the sky seems vaulted. 



