32 CELL-FORMATION. [BOOK i. 



primordial utricle divides into distinct portions and becomes 

 detached from the cell-wall before it begins to secrete mem- 

 brane, or that the new cells formed within the parent-cell, 

 subsequently become free by the solution of those layers of 

 membrane deposited immediately upon the primary walls." 

 (Ibid, where there is an excellent set of figures.) 



E. There is produced among mucus a Cytoblast, nucleus, or 

 central point, which acts chemically upon the matter in contact 

 with it, until it forms a firm layer. This layer is a closed 

 bladder, or vesicle, which enlarges by assimilating the fluid, 

 and becomes a cell, to whose inside wall the Cytoblast, which 

 does not grow to the same extent, remains attached, in the form 

 of a circular space or disk. This theory, which may be 

 regarded as an attempt at explaining original cell formation, 

 rather than the later forms of cell multiplication, originated 

 with Schleiden, who first knew how to apply a curious dis- 

 covery made by Francis Bauer. 



In the centre of some' of the bladders of the cellular tissue 

 of many plants there is a roundish body, apparently consist- 

 ing of granular matter, the nature of which is unknown. It 

 was originally remarked by Francis Bauer, in the vesicles of 

 the stigma of Phaius Tankervillise. A few other vegetable 

 anatomists subsequently noticed its existence; and Brown, 

 in his Memoir on the mode of impregnation in Orchids and 

 Asclepiads, has made it the subject of more extended observa- 

 tion. According to this botanist, such nuclei not only occa- 

 sionally appear on the epidermis of some plants (Plate III. 

 fig. 9.), in the pubescence of Cypripedium and others, and in 

 the internal tissue of the leaves, but also in the cells of the 

 ovule before impregnation. It would seem that Brown con- 

 siders stomates to be formed by the juxtaposition of two of 

 these bodies, which he calls nuclei, a term that usually belongs 

 to the ovule. (See also Slack, in the Trans. Soc. Arts, xlix.) 

 Schleiden has published some extremely interesting observa- 

 tions upon this body, which he regards as a universal elemen- 

 tary organ, and calls a Cytoblast. According to him, the 

 form varies from oval to lenticular and round, the colour 

 from yellowish to a silvery white, changing to pale yellow up 

 to darkest brown upon the application of iodine : in size it 



