214 THE LIFE OF THE PLANT 



is like a whole bladder, this increasing volume of cell- 

 sap will press on the wall and oblige it to stretch — to 

 grow. The protoplasm meanwhile will go on producing 

 on its external surface adjacent to the cell -wall fresh 

 quantities of cellulose. 



That cellulose is formed by the protoplasm is proved 

 by the following neat experiment. We cut a living 

 cell under the microscope, and let part of the proto- 

 plasm out into water. This protoplasm, like any other 

 liquid in a free state, assumes a spherical form, and 

 in a short time produces cellulose on its surface, 

 transforming itself into a new cell. It is most curious 

 that only those portions of protoplasm which contain a 

 nucleus possess this property of forming new cells. There 

 is a similar close connexion between the growth of cells 

 and the nucleus. During the normal growth of cells 

 a close relation is observed between the protoplasm 

 and nucleus and the formation of cellulose. During 

 this process the walls are thickened either uniformly all 

 over their inner surface, or only at certain parts of it, 

 and this depends on the relative positions of the proto- 

 plasm and the nucleus. 



On the strength of what has been said, the process of 

 growth comes to this. A mixture of substances, called 

 protoplasm, consisting mainly of albuminoids, in break- 

 ing down and undergoing chemical transformation, on 

 the one hand, gives rise to substances that dissolve in 

 the cell-sap and osmotically attract water — hence the 

 increase of the vacuole and the stretching of the cell- 

 wall ; on the other hand, owing to the same breaking 

 down of the protoplasm cellulose is formed, i.e. the 

 material with which the walls of a growing cell are built. 

 If our explanation is correct, on reversing the conditions 

 we shall get a phenomenon contrary to growth, i.e. 

 instead of an increase a decrease in the size of the cell, and 

 particularly of the vacuole and the protoplasmic bladder 

 distended by it. This conclusion is in fact supported 



