2 M. Mohl on the Circulation of the Sap 



cells are on the point of being formed, and at which the nuclei 

 have already made their appearance, as the centres of the future 

 cells, we find that the future mother-cell never contains a trans- 

 parent aqueous sap, but that a viscous colourless mass, mixed with 

 minute granules, is diffused in greater or less quantity through the 

 cellular space, and is especially concentrated in the vicinity of the 

 cell-nucleus, so that very frequently the outlines of the nuclei 

 appear through this mass but very indistinctly, and cannot be 

 seen accurately without the use of iodine. That this mucous 

 mass which is found in the cavity of the cell previous to the 

 occurrence of the nuclei is the material for the formation of the 

 cellular nuclei (they are coloured yellow by iodine precisely in 

 the same way as the fluid mass) can scarcely be doubted : but 

 whether the nucleus, as Schleiden supposes, is formed simply by 

 the union of the globules floating in the mucous fluid, or whether, 

 which is my own opinion, it is not rather an organic formation 

 increasing by intus-susception which is sharply bounded exter- 

 nally by the mucous fluid, has not yet been determined sufficiently 

 by microscopical observations, and we are unacquainted with any 

 chemical data capable of affording assistance in this examination, 

 both the chemical constitution of the globule and that of the 

 nucleus itself not being satisfactorily explained. It certainly 

 however deserves to be remarked, that according to the inves- 

 tigations of Mulder and Harting, neither the nucleus nor the 

 primordial utricle can be regarded as proteine compounds, a3 

 they are frequently imbued with proteine, but are also met with 

 perfectly free from it, and consist of a substance which it is 

 true cannot yet be well characterized chemically, but which is 

 distinct from the other solid structures of the cell. Precisely in 

 the same way as a separation occurs interiorly between the vis- 

 cous mass mixed with granules and the solid substance of the 

 nucleus, does the formation of the primordial utricle likewise 

 appear at the periphery to proceed from this mucous fluid ; but 

 as it is not my object to enter at present upon an examination 

 of the primordial utricle, and the question whether it should be 

 considered as an independent membrane, or as a layer of the 

 above fluid merely coating the walls of the cell, having treated 

 of those questions on a former occasion, I shall reserve some 

 further observations on this subject for a future paper, and shall 

 confine myself for the present to the consideration of the phe- 

 nomena which are observed in the semifluid nitrogenous sub- 

 stance diffused in the cavity of the cell. 



Since, a3 we have already observed, this viscous mass every- 

 where precedes the first solid formations indicative of future 

 cells where cells are to be formed ; since we must moreover admit 



