

66 FLOWERING PLANTS 
1. On the outside the dermatogen, which gives rise generally 
only to the root-cap. 
2. In the centre the plerome, which forms the stele. 
3. On each side of the plerome the periblem, giving rise to 
the cortex, the innermost layer of which forms the endo- 
dermis. 
Structure A transverse section of a typical Dicotyledonous 
Fees root, made a little behind the growing point (such 
_ Section. as that drawn in Fig. 35), shows the follow- 
ing tissues : | 
(a) An outer layer corresponding to the epidermis of the 
stem ; this is called the piliferous (Lat. pilus, a hair) layer in 
the root, because it bears 
hairs which are very 
conspicuous a little be- 
hind the tip. 
(0) Within that the 
cortical parenchymatous 
tissue, the inner layer 
of which is the endoder- 
mis, easily distinguished 
by the thickening of its 
side walls. 
(c) The stele consists 
of -:(1.). The: perteycle:; 
(ii.) vascular tissue ; 
Fic. 35.—Dicoryneponovs Root, Trans- (il.) pith. In a Dico- 
VERSE SECTION. (High power.) tyledon the typical num- 
p.t, piliferous layer ; cort, cortex; end, per of bundles in the 
endodermis ; p.f, pericycle ; w, wood ; 
b, bast ; p, pith. root is four ; they con- 
sist of groups of cells, 
forming bast and wood, arranged alternately. As these 
groups of cells le on alternate radu, the arrangement 
of the bast and wood is said to be radial. In a young root 
the wood is more distinct than the bast, and is nearer the 
centre. 
If sections are made further from the apex, so as to pass 


