40 MERISTEM. [CH. Ill 



entiated cells, which will in time give rise in their turn 

 to root on one side and root-cap on the other. This 

 tissue makes up what is known as the growing point of 

 the root and of the cap. Several things have to be noticed 

 about meristematic tissue : one is what may be called 

 the quality of perpetual youth. Let ABGD, fig. 15, be a 

 meristematic cell, and let it be divided into two com- 

 partments by the transverse cell-wall ab. The lower half 

 will give up its embryonic character and will begin to 

 make part of the permanent plant-body. But the other 

 half AabB retains the embryonic merismatic character, 

 and when it has again grown to its original size 

 it again divides by a line cd. The process may be 

 repeated indefinitely, so that we get a row of cells of 

 which the topmost retains the capacity of continued 

 division and all the rest are on the way to become 

 permanent tissue. 



I began by speaking of M (fig. 14) as a manufactory of 

 cells, and this is a convenient expression, but it must 

 always be understood that in such a manufactory, cell 

 originates from cell, and that the process of manufacture 

 is cell division of such a sort that half the divided cell 

 remains capable of keeping the work going. 



In thinking over the growing point of a root we are 

 liable to fall into a false conception; we think of cells 

 being manufactured one on the top of the other like 

 bricks which make up a wall, and we may imagine, 

 when the new layers of cells have been made and laid on 

 the older layers, that they have done their work, that they 

 have increased the size of the plant by their diameter, just 



