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MERISMATIC OR FISSIPAROUS CELL-FORMATION. 775 
may grow and divide in a similar way, and thus by the con- 
tinued growth and division in lke manner, of successive cells, 
all increase in the mass of the different parts and organs is due. 
This method of division is now often spoken of as direct, in con- 
tradistinction to the indirect method described further on (see 
p- 778). (it should be noticed that the primordial utricle of 
Mohl here referred to differs from that defined at page 26 of 
this Manual. Thus, according to the views adopted in this 
volume, the primordial utricle is characterised as the thin layer 
of protoplasm enclosing the watery cell-sap, and which lines 
the cell-wall after the cell has grown too large to be filled by 
protoplasm alone ; while Mohl regards it as a more or less 
thickened layer of protoplasm, having the appearance of a 
membrane lining the cellulose wall, and enclosing the ordinary 
protoplasmic contents of the cell.) 
Cell-division is best observed in water-plants of a low grade of 
organisation, and in hairs. In very simple plants also, such as 
Palmella, in which the newly formed cells separate and become 
independent plants, the process of division is well seen ; but in 
the higher plants, where they remain permanently united to form 
tissues of greater or less solidity, it is demonstrated with ditticulty. 
In this mode of cell-formation, it is by no means evident 
what function the nucleus performs. That iw some cases it is 
unimportant is clear, because cell-division, as above described, 
may take place, as it does in some of the lower orders of planis, 
without the presence of a 
nucleus. In the higher Pia, 1132. 
orders of plants, however, 
the original nucleus of 
the cell appears to under- Fie. 1131 
go subdivision into two ee Q 
halves, as is the case with ee cane O 
the other contents, so that =, Ce ; 
a nucleus is thus formed = “> Ses. = Q 
for each new cell into OP) = ag 
which the parent cell has 
been divided. But in 
other cases, separate nu- 
clei are formed for the _ 
secondary cells. instead of Fig. 1131. Yeast plant in process 
ak 9 : of development. Fig. 1132. 
the original nucleus di- Congerva glomerata, showing the 
viding into two. progressive stages of gemma- 
2 tion or budding (0, c, d,e). a. 
J. 
_ In some of the lower Terminal cell. (After Mohl.) 
kinds of plants, a modi- | 
fication of the above 
described process of cell-division takes place especially as 
a method of reproduction ; this consists in the formation of 
secondary cells, as little bud-like prominences on the primary 
cells, either at their extremities, as in the Yeast plant (jig. 
