METABOLISM 269 



condition is followed by the granular one, and in this state 

 the cell can remain for some time before the enzyme is 

 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 nuclei. This plate soon under- 

 goes 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. 



