DEVELOPMENT OF ROOTS. 798 
The cells composing it consist of primary meristem ;* they are 
thin-walled, filled with protoplasm, and are capable of division. 
Here, as in stems, and unlike leaves, the last formed part is 
. towards the apex ; hence the growth in length is indefinite, the 
difference between the growing part or so-called apical cell in 
roots (fig. 1144, v) and stems being that, in the former case, it 
or they (for there is (fig. 1145, a) usually a group of apical 
cells) are covered by a cap of cells formed from the distal or 
Fre. 1145. 
Fig. 1145. Polygonum Fagopyrum. Root apex, median longitudinal section. 
pe. Pericambium, outside boundary of the plerome. v. Rudiment of 
a vessel. e. Dermatogen. Between pe and e, periblem. h. Root-cap or 
pileorhiza. «a. Apical cells. After De Bary. 
apex end of the so-called apical cell (figs. 1144, k, 1, m, n, and 
1145, h) ; whereas in stems there is no such cap. (See page 
795, and figs. 1146 and 1147.) 
2. OF THE STEM oR CavuLoME.—The offices performed by 
the stem and its ramifications are :—1. To form a support for 
the leaves and other appendages of the axis which have but a 
* This name is given to that kind of meristem which forms the whole 
tissue of very young organs or parts of organs, in order to distinguish it 
from another kind of meristem, which is termed secondary meristem (as 
the cambium cells), which occurs in organs along with permanent tissue, or 
that tissue in which the cells are no longer capable of division, but have 
assumed their definite form. 
