CELLULAR TISSUE. 29 



Mohl's view.* The gelatinous nucleus of the cell often remains 

 adherent to some part of the wall, where its vestiges frequently 

 appear as a dark spot after the cell is full grown. Otherwise it 

 lies free in the cavity, the forming cell-wall being disengaged from 

 it on every side ; and sooner or later it is dissolved or absorbed. 



29. Without an antecedent Nucleus. Some observers do not 

 admit that the nucleus plays an essential part in cell-formation, or 

 that it exists in the first instance. Nor does it have a place in 

 Schleiden's account of the formation of free cells in fermenting 

 fluids, viz. : t "A globule of nitrogenous substance originates ; 

 in this a cavity is formed, it grows, and the complete cell has a 

 delicate coat of cellulose, without our being able to determine 

 the epoch of its production." | 



30. Multiplication of Cells, It is not by original cell-formation, 

 however, but by .the multiplication of cells already existing, that 

 the fabric of the vegetable is built up. A cell once originated, in 



* In Botanische Zeitung, Vol. 2, 1844. The abstract of Mohl's view is. thus 

 rendered, in the Appendix, I. c. p. 571, translated from Schleiden's 3d ed. : 

 "In all vitally active cells a living membrane occurs, consisting of a nitroge- 

 nous layer; this membrane exists earlier than the cell-wall formed of cellulose, 

 and therefore Mohl calls it the ' primordial utricle.' The new cells proba- 

 bly originate by the solution of the old primordial utricle, and the formation 

 of several new ones effected through a nucleus, which always precedes the 

 cell-formation." 



t Schleiden, in App'x to Engl. TransL, I. c. And Nageli, as rendered in an 

 abstract by Schleiden, I. c. p. 572. " 1. There is a free cell-formation without 

 a nucleus in certain of the lower Alga?, and in the formation of the spores of 

 Lichens and Fungi. Sometimes a nucleus is subsequently produced in the 

 completed cell. 2. Perfectly homogeneous globules of mucilage are formed, 

 the nucleoli; around these a perfectly homogeneous nucleus, on which a 

 proper membrane is soon to be distinguished. A homogeneous layer of mu- 

 cilage is deposited around the nucleus ; this gradually becomes thick, espe- 

 cially at one side; then granular in the interior; next it is enveloped by a 

 membrane, and the cell with a parietal nucleus is complete." On the other 

 hand, " Hoffmeister holds that, in the formation of a nucleus, a spherical drop 

 of mucilaginous fluid becomes coated by a membrane, and thus individualized, 

 without the presence of a corpuscle of denser substance (a nucleolus) inside 

 the spherical mass of mucilage either being essential or contributing to the 

 process." Henfrey, Bot. Gazette, 1. p. 128. 



I There seems to be little real discrepancy between this view and those of 

 Grew, Bauer, Mirbel, linger, and Endlicher, which agree in this ; that cells 

 originate as cavities in a mucilaginous matrix, and at length acquire inde- 

 pendent walls. 



3* 



