ROOTS. DE 
(c) The woody cylinder which forms the central portion of the root. 
The distinction between (b) and (c) is more evident when the section 
has been exposed to the air for a few minutes and changed somewhat in 
color. It is a good plan to look with the low power first at a thick 
section, viewed as an opaque object, and then at a very thin one mounted 
in water or glycerine, and viewed as a transparent object. 
Observe the cut-off ends of the ducts, or vessels, which serve as pas- 
sages for air and water to travel through ; these appear as holes in the 
+ Fria. 19. — Magnified Cross-Section of a very Young Exogenous Root. 
w, root-hairs with bits of sand adhering ; r, parenchyma cells of the bark}; e, inner- 
most layer of the bark; b, bast; h, vessels; c, c’, cambium. 
section, and are much more abundant relatively in the young than in the 
older and larger portions of the root. Sketch one section of each kind. 
Examine with a higher power (100 to 200 diameters), and note the 
ends of the thick-walled wood-cells. Compare these with Fig. 19. 
Notice the many thinner-walled cells composing stripes radiating away 
from the centre of the root. These bands are the medullary rays, whose 
mode of origin is shown in Fig. 52. Moisten some of the sections with 
iodine solution,! and note where the blue color shows the presence of 
starch. Split some portions of the root through the middle, cut thin 
11f the roots are in their winter condition. 
