H. VON MOHL ON CELLULOSE. 115 



with sulphuric acid, under which circumstances the outer mem- 

 brane presents itself unchanged with a yellow colour, after the 

 rest of the cell-membranes have been dissolved. The separation 

 of the cells seemed rather to depend upon the outermost layer 

 of the secondary membranes becoming softened into a gelatinous 

 condition, and detached from the primary membrane. The cir- 

 cumstance that the outer layers of the cells are caused to swell 

 up and dissolve in strong acid sooner than the inner, is not un- 

 commonly met with, especially in treating with sulphuric acid 

 half gelatinous cells saturated with iodine, for example, the half 

 collenchymatous cells of the bark, like those of Erythrina cqffra. 

 In such cases it is very common for the outer layers of the swollen 

 cells to have a brighter blue colour than the inner, and when by 

 a longer action of the acid these inner layers also become per- 

 fectly blue, the outer layers are completely bleached. A similar 

 phaenomenon sometimes presents itself most distinctly under a 

 strongish action of nitric acid. This is especially the case with 

 the wood- cells of Clematis Vitalba, the outer layers of which, 

 when the boiling in acid is long continued, dissolve into an 

 amorphous jelly, which acquires a blue colour with iodine. Such 

 a perfect solution of the outer layers, however, is by no means 

 necessary to bring about the separation of the cells; even a slight 

 softening of the cell-membrane seems sufficient to separate the 

 secondary layers from the outer membrane, and thereby the 

 cells from each other. In favour of this, we have both the 

 microscopic examination of cross sections which have been boiled 

 in nitric acid till the cells have separated, and in which fragments 

 of delicate torn membranes, but no amorphous jelly, are met with 

 between the cells, and also the circumstance, that in the wood 

 of Abies pectinata, which had been macerated for about a year in 

 dilute nitric acid, and in which the elementary organs fell apart 

 on the slightest pressure, the canals of the pits were closed at 

 the outer ends by a thin membrane, which could not have been 

 the case if the outer membranes of the cells had been dissolved. 

 The extraordinary softness which the cell- membranes had ac- 

 quired, both in this wood and in the hard vascular bundles of 

 the black-fibred palm above-mentioned, when treated in the 

 same way, was remarkable. 



In this separation of the cells, the outer coat never seemed to 



8* 



