774. CELL-DIVISION OR MERISMATIC CELL-FORMATION. 
only take place in the protoplasm contained in the intericr of 
cells forming parts of living tissues. 
B. CELL-piviston.—-This mode of cell-formation has been 
also called by authors merismatic or fissiparous cell-formation. 
Cell-division can only take place in cells in which the contained 
protoplasm is in an active state, as in the cells of the meristem, 
a name given to that kind of parenchyma the constituent cells 
of which are capable of multiplying by division (see page 88). 
It may be treated of under two heads: namely (1) Cell-division 
without absorption of the walls of the parent cell; and (2) Cell- 
‘division with absorption of the walls of the parent cell, and the 
setting free of the new cells. 
a. Cell-division without absorption of the walls of the parent 
cell.—This mode of cell-formation was first observed by Mohl, 
whose opinions were afterwards ably supported by Henfrey and 
Mitscherlich. According to these physiologists (and their 
observations have now been confirmed in all essential particulars 
by subsequent observers), this process is the one by which all 
the vegetating or growing parts of plants, whether Flowering 
or Flowerless, are produced and increased ;—all increase in 
the mass of the different organs is therefore due to its agency. 
The manner in which it takes place is as follows :—the proto- 
plasm of the cell, or, according to Mohl and Henfrey, the 
primordial utricle, becomes gradually constricted on the sides 
Bre. 11303 
Fig, 1130. a. Cell of Conferva glomerata, with the cell-contents constricted 
by the half-completed septum. 6. A half-completed septum in which a 
considerable deposition of cellulose has already taken place. c. A septum 
in course of development, after the action of an acid, which has caused 
contraction both of the primordial utricle (0), and the cell-contents (). 
d. Complete septum split into two lamelle by the action of an acid. 
(After Moh] and Henfrey.) 
so as ultimately to form a sort of hour-glass contraction, and 
thus to divide the original contents into two distinct portions 
(fig. 1180 a, b, c, d). Each portion of the protoplasm or of the 
primordial utricle then secretes a layer of cellulose over its 
whole surface ; and where this is in contact with the original 
wall of the primary cell it forms a new layer interior to it ; but 
where away from the wall, at the new septum, a distinct cell- 
wall, so that the partition is double. The original cell thus 
becomes divided into two, and forms two cells, each of which 
