M. Mohl on the Growth of Cell-Membrane. 265 



by this intermediate ligneous substance, or that the intermediate 

 ligneous substance is deposited on the outside of the oldest and 

 innermost layer (the cellulose) ; while Harting assumes that this 

 encrusting matter does not replace the cellulose, but permeates the 

 cell-wall composed of cellulose from within outwards and accumu- 

 lates in preference in its outer layers. This intermediate ligneous 

 substance is always combined with proteine. As analogous to 

 this deposition of intermediate ligneous substance, as the inter- 

 mediate layers of wood- and bark-cells and as the outer layer of 

 medulla-cells (in which latter Mulder did not find the outer 

 ligneous layer), other encrusting matters occur in the cells of 

 particular organs, for instance pectose in the so-called Collen- 

 chyma, and in the milk-vessels a substance partly isomerous with 

 vegetable mucilage, partly with cellulose, in the cells of the horny 

 albumen of AlstrGemeria, Iris, Phytekphas, &c. 



The conclusion which Harting and Mulder draw from the che- 

 mical facts here mentioned, with regard to the development of 

 cell-membrane, goes to establish the opinion, that those layers, 

 which in the membrane of a full-grown cell are characterized by 

 a peculiar chemical reaction, not yet presented by the membrane 

 of young cells, have been formed subsequently to the membrane, 

 consisting of cellulose, of the young cell, and that since these 

 layers occur on the outside of the full-grown cell (the inmost 

 layer of which is composed of cellulose, and therefore corresponds 

 to the membrane of the young cell), the cell-membrane has in- 

 creased in thickness in consequence of the subsequent deposition 

 of layers, differing chemically, from within outwards. 



Let us examine whether these conclusions be not too hasty. 

 It does not admit of the slightest doubt, that the chemical com- 

 pounds which are coloured yellow by iodine and sulphuric acid, 

 and which characterize the outer and intermediate layers of most 

 full-grown cells, are of later origin than the cellulose which forms 

 the membrane of the young cell. From this fact however it is 

 a great leap to the assumption, that these layers, which are com- 

 posed of a substance differing from cellulose, are in reference 

 to their situation also newly-formed layers, which are wanting 

 in young cells. This is quite possible ; but it is also possible, 

 that the fact as shown by anatomy is altogether otherwise. 

 If we first of all disregard totally the above distinct anatomical 

 facts, we may, with quite equal right to that by which an ex- 

 ternal formation of a new layer is inferred, guess, that in a layer 

 of the cell originally consisting of true cellulose, subsequently, 

 and without any alteration of its relations of position, the cel- 

 lulose is absorbed and replaced by an essentially different che- 

 mical compound ; or that the cellulose remains and a new com- 

 pound is deposited between its molecules, and prevents more or 



Ann. $ Mag. N. Hist. Vol xviii. U 



