II. vox MOHL ON CELLULOSE. 109 



In reference to the characters of thin membranes, the liber- 

 tells generally approach to the parenchyma-cells, since ordina- 

 rily they do not possess either the great solidity and brittleness, 

 or the dark colour which distinguishes most wood-cells. This 

 greater resemblance between the liber-cells and parenchyma- 

 cells presents itself also in their behaviour to sulphuric acid and 

 iodine, since the former mostly assume a pure blue colour with 

 these reagents. On the other hand, the liber-cells of the arbo- 

 rescent Monocotyledons, especially of the Palms possessing 

 hard vascular bundles, are aUied to the wood-cells of the Dico- 

 tyledons ; they are devoid not only of the softness and flexibility 

 which distinguish the liber-cells of many Dicotyledons, but in 

 many cases they exhibit also a yellow colour, sometimes passing 

 into the deepest brown. I examined the liber-cells of three 

 species of Palm, Cocos boti^yophora, Calamvs, and the black- 

 fibred Brazilian palms, the wood of which is used for making 

 walking-sticks. When a cross- section of the liber-bundle of one 

 of these is treated with iodine and sulphuric acid, the secondary 

 layers are dissolved and the outer layer of the cells remains be- 

 hind undissolved, with a brown colour. This outer layer, which, 

 like the above-described outer layer of the pith-cells of Clematis, 

 corresponds, according to the characters given by Mulder, to 

 the " outer wood-membrane " of the w^ood-cells of the Dicoty- 

 ledons, and would be supposed to consist of a substance different 

 from cellulose, exhibits considerable thickness in a cross section, 

 and in Cocos botryophora (where it is about xttW^'^ ^^ ^ ^^^^ 

 thick) is distinctly pitted. For these two reasons we cannot 

 regard it as the primary membrane of the cells, since in all 

 'cases its not inconsiderable thickness and the presence of pits, 

 which do not perforate the membrane completely, but penetrate 

 only to a certain distance on both sides, lead us to conclude that 

 this layer is composed of several superincumbent lamellae. When 

 a cross section of a vascular bundle of these plants boiled in 

 nitric acid is treated with iodine, exactly the same phaenomena 

 present themselves as I have described in the pith-cells of 

 Clematis, namely, all the layers of the liber-cells, especially the 

 outer one withstanding sulphuric acid, are coloured bright blue, 

 which proves that this latter also is composed of cellulose. If 

 vlilute sulphuric acid is then added to such a preparation, not 



