M. H. V. Mohl on the Structure of Chlorophyll. 323 



compelled to compress a summary of a large proportion of the 

 physiology of plants into a few sheets. 



A very important part of this doctrine of the organization of 

 the utricle, proposed by Nageli, has been retracted by himself 

 recently, since he acknowledges (Systemat. Uebersicht der Er- 

 scheinungeii im Pflanzen-reiche, 1853, p. 15) that he was wrong 

 in ascribing to the utricle a membrane composed of cellulose. 

 With this, however, he did not give up the opinion that the 

 chlorophyll-granules are utricles and structures analogous to 

 cells, but, on the contraiy, finds it inconceivable that in the year 

 1850 I had not yet detected the membrane of the cell-nuclei and 

 chlorophyll-granules, — since this, if we might be in doubt as to 

 its presence in fresh granules, presents itself so distinctly when 

 these structures swell up in water. 



In this later treatise Nageli explains the origin of the mem- 

 brane in a manner which stands in most glaring contradiction 

 to his earlier views on the nature of an independent membrane 

 and on the necessary properties of the utricle. He takes his 

 stand namely upon the phenomenon, that the surface of the 

 proteiuous structures occurring in the cell-sap exhibit a mem- 

 branaceous consolidation through the action of the cell-sap 

 where they are in contact with it, as for example the vacuoles 

 full of cell-sap, the protoplasm-currents, &c. According to his 

 view, the primordial utricle originates, in free cell-formation, 

 through this action of the cell-sap, by condensation of the super- 

 ficial layer of a semi-fluid proteine-compound ; and in like 

 manner hardens the surface of minute portions of proteiue- com- 

 pounds, which are to be converted into nuclei, chlorophyll-gra- 

 nules, &c. These latter structures correspond completely there- 

 fore, excepting in the want of the cellulose-coat, to cells, only 

 they are arrested at a lower stage of development. 



In this theory we have two points to take into consideration : 

 1. the question whether the outer, firmer surface of a soft 

 substance, which forms the boundary of the medium with which 

 it is in contact, is to be regarded as a membrane, and whether 

 the soft substance becomes a utricle through the formation of 

 this firmer limiting portion ; and 2. whether this firmer layer of 

 a nucleus, of a chlorophyll-granule, or the like, is comparable 

 with the primordial utricle. 



The first question must be answered most decidedly in the 

 negative ; indeed Nageli himself spoke most definitively against 

 this, so long as he believed in the presence of a cellulose mem- 

 brane clothing the granule. If indeed it were really a fact, that, 

 as Nageli now (System. Uebersicht, p. 16) states, the microscope 

 demonstrates on many mucilaginous filaments or masses, and 



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