322 M. H. V. Mohl on the Structure of Chlorophyll. 



To come to a clear understanding, therefore, it will be first of 

 all necessary to consider the notion of th^ utricle, as laid down 

 by Nageli ; and this is the more requisite, since his definition 

 of it deviates most essentially in several particulars from the 

 usual signification of the word in common language. According 

 to Nageli's definition, it is on the one hand unnecessary that an 

 organic utricle should be hollow, while on the other, a hollow 

 space occurring in the cell-contents, even when surrounded by a 

 membrane, is not in all cases to be called a utricle ; but it is an 

 essential part of the notion of the latter, that, like the cell, it 

 possesses a proper membrane and contents which exhibit pecu- 

 liar changes. According to this definition, a vacuole in the pro- 

 toplasm, filled with water, even if the mucilaginous fluid bound- 

 ing the cavity is condensed through the influence of the water, 

 and forms as it were a membrane, is by no means to be called 

 a utricle ; and still less may we apply this name to a globular 

 mass of proteinous substance, the outermost layer of which is 

 hardened into a membrane-like coat, when such a body occurs 

 in the cell-cavity. The decision of the question, whether a 

 structure occurring in the vegetable cell is a utricle, depends 

 rather, according to Nageli's view, on the investigation whether 

 this consists, like cells, of a membrane and contents of difierent 

 nature from the membrane, and whether it exhibits altogether, 

 in reference to membrane and contents, metamorphoses ana- 

 logous to those with which we are acquainted in cells. 



Nageli believes that he has found these properties, character- 

 izing the utricles, displayed most convincingly in nuclei, starch- 

 granules, chlorophyll-granules, and other granulose structures 

 occurring in cells. He states that these possess, like cells, a 

 colourless membrane composed of cellulose, which originates 

 subsequently to the contents, increases in thickness, like the 

 cell-wall, by lamellar deposits in the interior, divides by the for- 

 mation of daughter-utricles, &c. ; in short, he holds the struc- 

 ture of the utricle to correspond completely to the organization 

 of the cell, and the only distinction he finds between utricle and 

 cell is, that the former contains no cytoblasts, and, as a struc- 

 ture enclosed in the cell, is not an immediate, but merely a 

 mediate or indirect elementary organ of the plant. 



As in my researches on chlorophyll- granules, just as in nuclei, 

 starch-granules, &c., I could find neither a membrane distinct 

 from the contents, nor, still far less, a cellulose coat comparable 

 to the cell-membrane, I expressed myself, in my " Elements of 

 the Anatomy and Physiology of the Cell,'' against this utricular 

 theory, as a representation standing in most decided contra- 

 diction to the facts ; that this was done in few words will be 

 understood from the circumstance, that in the said work I was 



