178 A TEXTBOOK OF GENERAL BOTANY 
this function because it is conical in shape, and probably even 
more so on account of the fact that the cell walls, or at least 
the middle lamelle of the old cells, become gelatinous. This 
makes the surface of the rootcap rather slimy, so that friction 
with the soil particles is greatly reduced and the tip can move 
through the soil more readily. As the rootcap is pushed forward 
through the soil particles the older cells 
are rubbed off and are replaced by 
younger ones which are produced from 
the meristem at the junction of the 
rootcap and the tip of the root. 
Grand period of growth. A portion 
of a root, like any other part of a 
plant, has a grand period of growth 
which can be divided into a phase of 
formation, a phase of elongation, and 
a phase of maturation. As has been 
said before, the cells that add to the 
length of the root are produced on the 
basal side of the growing point. After 
these cells are cut off from the growing 
point they undergo a limited number of 
divisions. The part of the root in which — 
division is most active is in the phase 
of formation, and the region in which 
this division occurs. may be termed the 
region of formation. After dividing a number of times the cells 
derived from the growing point cease to divide, and elongate very 
considerably (Fig. 183). The region in which this is taking place 
most actively is called the region of elongation, and the portion 
of the root that is elongating is in the phase of elongation. The 
greatest increase in length of any portion of a root occurs while 
it is in this phase. Fig. 13 gives an idea of the elongation of an 
individual cell. After a portion of a root has reached its mature 
length the cells in that part take on their final characteristics. A 
region in which this is occurring is in the phase of maturation. 

Fic.181. Tip of aérial root 
of Pandanus tectorius, show- 
ing rootcap 
Compare Fig. 196. (x 4) 
