Mr. Colebrooke on Jrrangernentsin Natural History. 43 



Art. IV. On Dkhotomous and Quinary Arrangements in 

 Natural History. By Henry Thomas Culebrookb^ 

 Esq,, FM.S., F.L.S., F.G.S., ^c. 



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

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

 " 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. 



