114 H. VON MOHL ON CELLULOSE. 



application of iodine ; while if the transverse section of a wood 

 is boiled longer than is requisite to impart to its cells the capa- 

 bility of acquiring a blue colour with iodine, under which cir- 

 cumstance the cells begin to separate from each other, the inter- 

 cellular substance is no longer found, being dissolved. I hoped 

 to find it in a transition state between these two extreme 

 cases, and then perhaps, if it contained cellulose, to be able 

 to detect this with iodine ; and, if I was not deceived, it indeed 

 happened with a few w r oods, for example, in Buxus sempervirens 

 and Clematis Vitalba, it assumed a bright blue colour after the 

 yellow had disappeared. This colour however was very pale, and 

 might possibly have depended on a bluish tinge thrown upon 

 the bleached intercellular substance by the surrounding dark 

 blue-coloured cells, so that I do not venture to declare the 

 observations certain, and must leave this point undecided for the 

 present. 



To mention some of the examples in which an intercellular 

 substance with the said properties filled up the intercellular 

 passages between the wood-cells, I may name Larix europcea, 

 Taxus baccata, Torreya taxifolia, Viburnum Lantana, Buxus 

 sempervirens, Clematis Vitalba. 



When the intercellular substance is dissolved by means of 

 nitric acid, the cells of the wood begin to part from each other. 

 It is difficult to trace accurately the process which occurs here, 

 since the blue colouring of the cell-membrane by iodine, which 

 would greatly facilitate the investigation, does not occur 

 unless the preparation saturated with iodine is allowed to dry 

 up ; but this drying causes a contraction and tearing of the 

 membranes, which places the greatest difficulty in the way of 

 detecting what goes on during the separation of the cells. The 

 notion might readily be formed that the separation of the cells 

 resulted from the solution of their outer membrane, as well as 

 the intercellular substance, by the nitric acid, and that the cement 

 which connected the cells together was thus removed. But if I 

 have rightly understood the operation, it is something quite dif- 

 ferent from this. The outer membrane is not dissolved, as is 

 easily seen when such preparations, saturated with iodine (whether 

 the cells have been separated from each other by boiling nitric 

 acid or by long maceration at ordinary temperatures), are treated 



