8 CAMBIUM MEMBRANE AND FIBRE. [BOOK i. 



to be nothing more than this universally distributed organic 

 mucus. An account of its composition and of the part which 

 it plays in the Vegetable Organisation, has been given by 

 Mirbel and Payen, (Comptes rendus, 1843, i. 98; Annales des 

 Sciences Nat., xix. p. 193). They describe this substance, 

 which precedes the appearance of cells, and is always present 

 where vegetable matter is in a state of growth, as containing 

 substances analogous to those which constitute animal bodies, 

 that is to say, including nitrogen. It is, however, also mixed 

 with other materials not azotised, composed of carbon and 

 the elements of water, such as dextrine, gum, starch, sugar, 

 glycose, mannite, &c. At the moment when vegetation is 

 renewed by the development of cells, unazotised cellulose 

 also appears, and increases by new layers, identical in their 

 chemical constitution, although sometimes other matters are 

 added to form woody tissue. From this kind of thickening 

 of cellulose, we can understand, say our authors, why wood 

 in the- interior of stems contains little nitrogen, while spon- 

 gioles, buds, and growing ovules, contain from ten to twenty 

 times as much. It may be, however, that, as Link says, the 

 word cambium is applied by Payen and Mirbel to secretions 

 essentially different, and that much more refined chemical 

 analysis is required to show that all intercellular or orga- 

 nisable matter is identical in composition. 



It is the opinion of some anatomists that of membrane 

 and fibre, the latter only is the basis of the tissue of plants : 

 fibre itself being a form of membrane ; or, which there is no 

 sufficient evidence to show, that all membrane is composed 

 of fibres interlaced. But we find both the one and the other 

 developed in many of the most imperfectly organised plants, 

 such as Scleroderma and other fungals, and it is difficult to 

 conceive how that can be a mere modification of membrane 

 which can be generated independently of it, which has no 

 external resemblance to it, and which in most cases is 

 obviously something superadded. Link observes that Mohl 

 has taken great pains to refute Meyen's assertion, that the 

 vegetable membrane is formed of spiral fibres. But in 

 reality the assertion had only a very limited application, 

 because by far the greatest number of membranes in the 



