METABOLISM 263 
discharged. When this has happened the hyaline condition 
is resumed. 
The formation of the cell-wall which separates the cells 
is due to a similar activity of the protoplasm. The division 
of cells or the development of new protoplasts will be more 
fully considered in a subsequent chapter ; it will suffice to 
say here that in all ordinary growing points this division 
of a protoplast into two is followed immediately by the 
formation of a new supporting membrane between them. 
The division of the cell is preceded by the division of 
its nucleus, which is attended by a series of complicated 
movements of particular constituents of its substance. The 
two daughter-nuclei are situated at some little distance from 
each other and are connected by a number of delicate fila- 
ments which are gathered to a point at each end and 
spread out in the centre, forming what is called the 
nuclear spindle. This generally stretches completely 
across the long diameter of the cell. 
During these introductory changes the hyaline proto- 
plasm becomes more granular, and the granules, technically 
spoken of as microsomata, are attracted to the spindle 
fibres. They pass along these fibrils from both regions of 
the cell and form a plate of extreme tenuity across it, 
midway between the two new nuclei. This plate soon 
undergoes a transformation, the granules disappearing and 
the membrane becoming translucent, and so forming the 
ordinary substance of the cell-membrane, generally, though 
perhaps not strictly accurately, known as cellulose. The 
cell-wall is thus seen to be formed from the protoplasm, or 
to be secreted by it, the granules or microsomata of which 
it is at first composed being the result of decompositions 
set up in the living substance. 
When cell-walls are growing in thickness or in surface 
a similar decomposition of the protoplasm can be observed. 
The microsomata or granules are formed in the proto- 
plasm and are gradually deposited, often in oblique rows, 
upon the original membrane. They are subsequently 
