108 H. VON MOHL ON CELLULOSE. 



filtrated either with a greater quantity of that substance, ac- 

 quiring a yellow colour with iodine, with which the inner layers 

 are saturated, or with some compound different from this, 

 opposing a greater resistance to sulphuric acid, which is so far 

 extracted or altered by nitric acid, that the reaction with iodine 

 occurs in the cellulose contained in this layer, but enough re- 

 mains to protect this layer from the action of weak sulphuric 

 acid, while in the outermost, immeasurably thin layer, the resist- 

 ance to sulphuric acid is so great that the latter is incapable of 

 dissolving it. 



In reference to the question whether the above-described outer 

 brown pellicle of the parenchyma- cells contained cellulose, the 

 behaviour of the primary membrane of the cells of the horny 

 albumen of Sagus tcedigera seemed to me of considerable im- 

 portance, since here I could convince myself not only of the 

 absence of a yellow colouring of this pellicle, as in the other 

 parenchyma-cells, but positively of its acquiring a blue colour. 

 When the membrane of these cells is treated with a very weak 

 tincture of iodine, it is coloured bright yellow, and the primary 

 membrane deep yellow ; in such a preparation very dilute sul- 

 phuric acid produces a very bright blue in the secondary layers 

 of the cells, and a darker blue in their primary membrane, and 

 under these circumstances, the comparatively great transparency 

 of the cellulose allows one to become quite certain of the purity 

 of this colour and of the total absence of that yellow colour in 

 the outer primary coat. If stronger sulphuric acid is added, the 

 secondary membranes are bleached and gradually dissolved, 

 while the primary membrane turns yellow and becomes coated with 

 fine granules*. Under these circumstances it cannot be doubted 

 that the primary membrane is imbued with a greater quantity 

 of the substance coloured yellow by iodine, but that this is in- 

 sufficient to prevent the appearance of the blue colour under the 

 action of iodine and weak sulphuric acid; yet its presence may 

 be the. cause why a stronger acid does not dissolve this mem- 

 brane, for it is always found that a membrane resists the action 

 of sulphuric acid more strongly in proportion as it is more deeply 

 coloured by it and iodine. 



* The granules, or minute drops (for there is no means of deciding whether 

 they are solid or fluid), are not separated until the sulphuric acid hcgins to act. 



