28 ANATOMY AND PHYSIOLOGY OF 



alone are generally deposited ; in wood-cells, on tlie contrary, first an 

 outer coat is formed, and then subsequently intermediate layers of consi- 

 derable tliickness are formed between this and the inner primary mem- 

 brane. 3, The new substances are deposited in the cell-wall of many 

 cells (in the horny albumen of PJiytehphas, Iris, and the so-called coUen- 

 chymatous cells), and therefore the wall does not exhibit lamellation. 

 The constitution of these different deposits is described as very varied. 

 Proteine is shewn to be merely an infiltrated matter, taking no part in 

 the formation of the cell-wall, and is wholly wanting, or only just trace- 

 able in very young cell-membranes j but it occurs in the intermediate 

 substance of all old wood-cells, and most old pith-cells, but not in bark- 

 cells or collenehymatous cells. The following compounds are p>articularly 

 noticed as forming definite layers of the elementary organs. Intermediate 

 wood-substance (the formula of which is stated at O40; Hse? 0%), a com- 

 pound which is coloured yellow by iodine and sulphuiic acid, swells up in 

 weak acid and dissolves in stronger ; it gradually displaces the celhilose 

 more or less perfectly in the secondary layer of vessels, forms the outer 

 layers of pith-cells and the intermediate of the wood-cells, in which it 

 becomes the more intimately combined with the cellulose the further the 

 layers he toward the inside. Bxlernal wood-substancej which is coloured 

 brown by iodine and sulphuric acid, and does not dissolve in the latter ; 

 it is stated as probable that this is isomerous with the intermediate wood« 

 substance, but (as in the woody matter of the putamen of hard fruits) is 

 distinguished from it by containing ulmin. It forms the outer layer of 

 wood-cells, scalariform ducts, and pitted vessels. Besides these more 

 generally distributed compounds, there occur other peculiar, less exten- 

 sively prevalent, compounds not yet fully characterized, one of which 

 formitL cuticle; a^oLr tLe cel/of corkfanotler the cJUs of the horny 

 albumen of Iris and Alstrmmeria. The following are regarded as incrust- 

 ing compoimds, penetrating into the substance of the cell-wall : pectose in 

 the cells of the collenchyma, of the Apple, &c. ; starch in Cetraria islan- 

 dica ; vegetable mucilage in Sphmrococcus crispua ; and a peculiar sub- 

 stance isomerous with cellulose, in the cells of the albumen of Fhytelephas. 

 My own investigations {^^Investigation of the question ' Does cellulose 

 form the basis of all vegetable membranes V^^—Botan. Zeit 1847, 497) com- 

 pel me to declare most distuictly against the view of Mulder's, that a 

 great proportion of the layers composing the membranes ai^e from the 

 first composed of compounds difierent from cellulose ; and also against 

 his opinion as to the relative ages of the layers, deduced from these pro- 

 positions (which I have already discussed above under an anatomical point 

 of view). I found that the application of iodine and sulphuric acid, in 

 which Mulder places such unconditional trust, is a means in the highest 

 degree unsafe for deciding whether a membrane contains cellulose or not. 

 My researches shewed me that the infiuence of sulphuric acid was by no 

 means necessary for the production of the blue colour in membranes which 

 are not strongly incrusted, as in the parenchymatous cells of succulent 

 organs, but that iodine and water alone are sufficient ; while in full-grown 

 and hardened cells sometimes the primary membrane alone, sometimes 

 even a greater or smaller portion of the secondary layers had, through the 

 deposition of foreign substances, altogether lost the property of becoming 

 blue on the application of sulphuric acid and iodine, although they were 



