GROWTH 105 
plasm actually does increase, or decreases but little. In 
other words the growth of the cell is mainly accomplished 
by absorbing large amounts of water, the cell wall being 
increased in area so as to keep pace with the increase in 
volume. It is possible that in some cases where the 
growth of the cell is very rapid the total amount of cyto- 
plasm in the cell may actually be reduced in manu- 
facturing the additional cell wall substance required. 
In this growth we can distinguish three phases which can 
be more or less clearly set off, viz., formative phase, phase 
of enlargement and phase of differentiation or maturation. 
149. Thus it comes about that at the growing root tip 
or tip of the stem we can distinguish an area near to the 
tip where growth is not very rapid but cell division is 
taking place abundantly (i.e. the cells are in the formative 
phase of growth), and another area into which the first 
grades, and a little distance back from it, where the cells 
are enlarging very rapidly and but little cell division is 
taking place (i.e. the cells are in the phase of enlarge- 
ment). This gradually grades off into that portion of 
the root or stem where growth in size is no longer oc- 
curring but where the various tissue differentiations are 
taking place (i.e. the phase of differentiation). In the 
root these zones are well marked, while in the stem the 
elongation may persist for a long while and may become 
localized in nodes while the internodes cease to grow. 
In this case the nodes usually retain some meristem and 
possess the power of producing new cells as well as in- 
creasing in size. 
150. There are several factors that influence plant 
growth. There must in the first place be sufficient food 
stuffs to enable the cells to manufacture the necessary 
new cytoplasm and cell wall. Then there must be 
sufficient organic substances to produce the osmotic 
