INTRODUCTION. 39 



organization, but also and mainly by chemical analysis. In 

 the 14th volume of the second series of the " Annales des 

 Sciences Naturelles (Botanique, 1840)" is an elaborate and 

 highly interesting memoir by M. Peyen, on the chemical 

 composition of vegetable tissue. In this memoir, M. Peyeii 

 establishes a distinction between animals and vegetables 

 based upon the chemical difference which he has ascertained 

 to exist between the cellular membranes of the respective 

 divisions 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 elementary 

 constituents 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 the 

 animal tissue or membrane, on the contrary, is as invariably 

 QUATERNARY, or formed of all the elementary constituents in 

 less fixed proportions. This generalization is arrived at by 

 an extensive and careful analysis, not only of animal sub- 

 stances, but also of examples of most of the families and 

 orders of Phanerogamic and Cryptogamic plants. Amongst 

 the freshwater Algce an analysis was made of Conf. rivularis, 

 Oscillatoria, and Chara, these all offering the same result as 

 the other analyses of vegetable tissue, and therefore being con- 

 clusive as to the vegetable character of the Confervoid division 

 of the Alg(B. It is to be regretted that an analysis was not 

 made of the DesmidecB and JDidtomea, with a view to de- 

 termine more certainly than has yet been done their position 

 in the scale of beings. That the Desmidece are really vege- 

 table productions, scarcely a doubt remains, iodine demon- 

 strating the presence of starch in abundance in the contents 

 of their cells. 



The following are the steps adopted by M. Peyen in order 

 to free the membrane of the Conferva rivularis and Oscillatoria 

 from all extraneous matter, and thus to prepare it for 

 analysis : 



" I tried next to test, with the same object in view, very 

 many Conferva. Soda, by dissolving with heat the investing 

 membrane of the filaments of Conferva rivularis, separated 



D 4 



