CHAPTER III 
ROOTS AND THEIR RELATION TO THE WORK OF PLANTS 
16. Structure of roots. We have already discussed the gen- 
eral nature of roots. Careful examination of a cross section 
of a young root shows that there is a definitely organized 
central cylinder, around which is the cortex, both well shown 
in figure 15. The surface layer of the 
cortex is the epidermis (fig. 16, e). The 
growing root tip is covered with several 
layers of dead or dying cells, which make 
up the rootcap. As the root pushes its way 
through the soil the rootcap is constantly 
being worn away on the outside. During 
the seasons of activity the rootcap is con- 
tinually being rebuilt by the formation of 
new layers of cells on its inner surface. 
In older roots the epidermis has given 
of central portion of Place to bark, which is composed of sev- 
root of sweet flag eral layers of cells. If a cross section of 
(Acorus) a very young root of a dicotyledonous 
heer mee sehen plant is examined with a moderate mag- 
cylinder; v, vessels of Mification, it will be seen that the cortex 
various sizes; 8, sieve is made up of rather loosely aggregated 
cells. Magnified 70 diam- ‘ . 7 
eters. After De Bary Cells, while the central cylinder is more 
closely compacted. In the cylinder are 
found a definite number of radially arranged fibrovascular 
bundles. The woody strands of these bundles alternate with 
strands of what are known as bast fibers, shown in figure 44. 
17. The root-hair cell. The general tubular structure of 
root hairs was very briefly explained in section 8. A root hair, 
20 
Fre. 15. Cross section 
