100 H. VON MOHL OX CELLULOSE. 



is marked with raised lines in many plants, as a proof that it is 

 not to be considered simply as a hardened excreted fluid, since 

 possibly those lines ought to be looked upon as a proof of definite 

 organization. 



The researches of Mulder and Harting have made known that 

 sulphuric acid and iodine do not demonstrate the existence of 

 cellulose in cork any more than in cuticle ; any one may readily 

 convince himself of the correctness of this statement in the cork 

 of the cork oak, of the elder, c. The cells also of the nascent 

 suberous layer, in their earliest condition, while still covered by 

 the epidermis, exhibit the same yellowish brown colour on the 

 application of the said reagents, as developed cork, even in those 

 plants in which the cork never attains any considerable develop- 

 ment, for instance in Cereus peruvianus. The conclusion drawn 

 from the absence of a blue colour, that the membrane of cork- 

 cells contains no cellulose, and is composed of a peculiar substance, 

 is, on the other hand, just as groundless as in the preceding case ; 

 for a thin section of the cork of the cork oak, which has been 

 boiled in solution of potash until the brown colour it originally 

 assumes has disappeared, acquires as bright a blue with iodine 

 as any other membrane composed of cellulose; in like manner, 

 and also by the application of nitric acid in the way described 

 below, the corks of Sambucus nigra, Acer campestre, Ulmus 

 campestris, and Euonymus europ&us, show that their cells are 

 composed of cellulose. 



It is well known that the layer to which I have applied the 

 name of periderm, is, in anatomical respects, to be regarded as 

 a modification of the cork-layer. This circumstance led me to 

 conjecture that this membrane would display chemical characters 

 similar to those of cork. This was confirmed. I subjected the 

 periderms of the oak, of Crat&gus Oxyacantha, Betula alba, and 

 Plosslea floribunda, to the action of a boiling solution of potash, 

 after which iodine produced the blue colour. The blue colour 

 was quite clear in the oak and Cratcegus, but in the other two 

 less pure; the periderm of Plosslea, indeed, did not require a very 

 long boiling in solution of potash to produce the blue colour, 

 but only isolated patches of the cells were coloured pure blue, 

 the greater part acquiring a dirty blue tint. The periderm of 

 the birch, which very obstinately resisted the action of the potash, 



