INTRODUCTION.
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organization, but also and mainly by chemical analysis. Inthe 14th volume of the second series of the “ Annales desSciences Naturelles (Botanique, 1840)” is an elaborate andhighly interesting memoir by M. Peyen, on the chemicalcomposition of vegetable tissue. In this memoir, M. Peyenestablishes a distinction between animals and vegetablesbased upon the chemical difference which he has ascertainedto exist between the cellular membranes of the respectivedivisions of the organic world. The vegetable tissue, M.Peyen finds, to exhibit invariably a ternary composition,that is, it is composed of three out of the four elementaryconstituents of which all bodies are formed, viz. carbon,hydrogen, and oxygen in nearly fixed proportions, as follows: —■carbon 44, hydrogen 6, oxygen 50. The composition of theanimal tissue or membrane, on the contrary, is as invariablyquaternary, or formed of all the elementary constituents inless fixed proportions. This generalization is arrived at byan extensive and careful analysis, not only of animal sub-stances, but also of examples of most of the families andorders of Phanerogamic and Cryptogamic plants. Amongstthe freshwater Alga an analysis was made of Conf. rivularis,Oscillatoria, and Chora, these all offering the same result asthe other analyses of vegetable tissue, and therefore being con-clusive as to the vegetable character of the Confervoid divisionof the Alga . It is to be regretted that an analysis was notmade of the Desmidea and Diatomea, with a view to de-termine more certainly than has yet been done their positionin the scale of beings. That the Desmidea are really vege-table productions, scarcely a doubt remains, iodine demon-strating the presence of starch in abundance in the contentsof their cells.
The following are the steps adopted by M. Peyen in orderto free the membrane of the Conferva rivularis and Oscillatoriafrom all extraneous matter, and thus to prepare it foranalysis : —
“ I tried next to test, with the same object in view, verymany Conferva. Soda, by dissolving with heat the investingmembrane of the filaments of Conferva rivularis, separated
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