96 II. VON MOHL ON CELLULOSE. 



since a particular layer of an elementary organ may undergo a 

 chemical metamorphosis in the course of time, without experi- 

 encing on that account any alteration in dimensions, or affording 

 cause for it to be regarded as a new layer in an anatomical sense 

 of the word : I stated that in respect to this metamorphosis we 

 have to consider two possibilities, since it might arise either 

 through the cellulose of which the layer was originally composed 

 becoming dissolved and replaced by some other chemical com- 

 pound, or through the persistent cellulose becoming saturated 

 by another compound, and hence losing the capability of reacting 

 with iodine and sulphuric acid. For various reasons I declared 

 the latter view, which certainly offers the most glaring contra- 

 diction to the views of the chemists, to be the more probable^ 

 but I could not distinctly prove it, because I was unable at that 

 time to extract the infiltrated matters from such membranes as 

 offered an obstinate resistance to the action of sulphuric acid and 

 iodine, and in which cellulose could not be demonstrated to 

 exist by the application of those reagents; such a process of 

 extraction being necessary to render the cellulose (which I 

 assumed to form the basis of the membranes) accessible to the 

 action of the iodine. Now, as the following pages will show, I 

 have succeeded in this with all the elementary organs of vege- 

 tables, and 1 therefore assert most distinctly that the walls of all 

 the elementary organs of plants are composed of cellulose ; that 

 it is quite inadmissible to draw conclusions as to the period of 

 origin of any given layer of their walls from its chemical condi- 

 tions, and that in regard to this question anatomical evidence 

 alone is valid. 



In order to establish this proposition, I am compelled to enter 

 somewhat minutely into the details of my investigation: if I 

 enter into more extended explanations of the methods I followed 

 than seems to many altogether necessary, this is to be attributed 

 to the circumstance that I only arrived at determinate conclusions 

 after many unsuccessful experiments, and I wish others to be 

 able to confirm the correctness of my views. 



Cuticle stands first of all the structures, in which it is impos- 

 sible to demonstrate a trace of cellulose by iodine and sulphuric 

 acid. It either completely withstands the action of sulphuric 

 acid, or, if it undergoes a certain degree of softening by this acid. 



