CELLULAR TISSUE. 31 



the spores of most Flowerless plants (101. 109), originate.* It is 

 subservient to reproduction, as these examples show, rather than to 

 vegetation. On the one hand, it might be ranked as a mode of 

 original cell-formation ; on the other, it passes by insensible grada- 

 tions into the next mode, where 



32. The cell is multiplied ~by the formation of a partition which 

 divides its cavity into two ; the original wall remaining. In this 

 way, a single cell gives rise to a row of connected cells, when the 

 division takes place in one direction only, or a plane or solid mass 

 of such cells, when it takes place in two or more directions ; thus 

 producing a tissue. It is in this way that all ordinary vegetating 

 or growing parts are produced and increased. The division is 

 effected, as before, by the annular constriction and infolding of 

 the mucilaginous lining of the cell (the primordial utricle of Mohl); 

 the circular fold meeting at the centre divides the contents into 

 two portions, and a layer of permanent cell-membrane, which is 

 somewhat later deposited upon each lamella of the fold, forms a 

 complete double partition ; thus converting one cell into two, and 

 so on.t 



33. Although connected in their origin, such cells may break 



* Some spores are produced by the condensation of the whole contents of 

 the parent cell and the acquisition of an investing cell-membrane, without any 

 division, as in Conferva glomerata, &c., or of the undivided contents of one 

 end of a cell, as in Vaucheria, Fig. 71. 



t This mode of cell-multiplication was first shown and most ably maintain- 

 ed by Mohl, as the universal mode of increase in growing parts. It has been 

 illustrated from independent observations by Henfrey, in a paper read before 

 the British Association at Cambridge, in 1846; and has recently received 

 new confirmation from Mitscherlich's researches upon the development of 

 Conferva glomerata, the plant upon which Mohl's observations upon cell- 

 division were principally made. Henfrey has given an abstract of Mitscher- 

 lich's paper in Ann. fy Mag. Nat. Hist., Vol. 1, new ser., 1848, p. 436. Schlei- 

 deh's statement of the process, as rendered by his English translator (p. 572), 

 is, " This fold of the primordial utricle is followed somewhat later by 

 a fold of the cell-membrane itself, which, finally arriving at the axis of the 

 cell, blends, and from the nature of its origin forms a complete double sep- 

 tum." But Mohl, Henfrey, and Mitscherlich appear to agree that the proper 

 wall of the parent cell is not constricted, only its lining or primordial utricle ; 

 and that "the septum is certainly a new structure, a double layer of membrane 

 formed in the fold," yet deposited, according to Mohl and Henfrey, " gradu- 

 ally from the circumference to the centre." " The layers of the partition are 

 therefore continuous with the layers of thickening in the interior of the lateral 

 walls," as Henfrey states. 



