118 H. VON MOHL ON CELLULOSE. 



power of reacting with iodine. These questions must be answered 

 by chemists, and not by botanists. Yet I may be permitted to 

 allude to two points. A conversion of the cellulose into starch 

 is out of the question, for the cell-membranes treated in the way 

 described remained afterwards, as before, insoluble in boiling 

 water; if therefore a transformation of the cellulose is assumed, 

 it must be into some compound as yet unknown, the characters 

 of which have still to be minutely investigated. For the present 

 the assumption of such a transformation appears to me unwar- 

 ranted, in so far that the power of the cell-membranes to acquire 

 a blue colour with iodine is the only reason at present existing 

 which can be urged in favour of this, while I have already shown, 

 on previous occasions, that fresh, perfect, unaltered cell-walls of 

 many plants, particularly of young organs, also acquire a blue 

 colour with iodine, which indicates that cellulose possesses this 

 quality, as well as starch, in and by itself, whenever its reaction 

 is not prevented by other compounds united with it. For the 

 present, and until we obtain further explanations from the 

 chemists, it will be simplest to assume that the potash and nitric 

 acid bring about this reaction by removing such foreign com- 

 pounds from the encrusted membranes. 



Looking from anatomical and physiological points of view, and 

 these alone I have occupied in my researches, I believe that I 

 have shown, from the latter, that the reaction of sulphuric acid 

 and iodine upon cellulose is altogether devoid of the trustwor- 

 thiness ascribed to it, and that the assumption based upon this 

 supposed trustworthiness, that particular layers are formed of 

 other compounds besides cellulose, in the course of the develop- 

 ment of the elementary organs of plants, and that the chemical 

 reaction of the different layers of a vegetable elementary organ 

 therefore affords a certain test of the relative epoch of its deve- 

 lopment, is totally devoid of foundation ; that, consequently, 

 all the objections against my theory of the development of the 

 walls of vegetable cells, built upon this basis, are completely un- 

 tenable, and that in this question anatomical evidence alone can 

 be admitted as proving anything. 



[A. H.] 



