48 SOUTH AFRICAN BOTANY 
stem there are dead, spongy cells, filled with air. Some- 
times they disappear. 
The vascular bundles of the stem (fig. 31) differ con- 
siderably from those found in the root. Each bundle 
CD O0) 
aK ATS 
ey 
te 
Ss 
Fic, 31.—Vascular Bundle of Helianthus tuberosus, the Jerusalem 
Artichoke. 
c. Cortex. e¢. Endodermis, /f. Pericycle fibres. s.t. Sieve tube. 
e.c. Companioncell, cb. Cambium, 4.cb. Interfascicular cambium. 
d.v. Pitted vessel. a.f. Xylem fibre. p.w. Spiralvessel. pp. Pith. 
m.rp. Medullary ray. (From Darwin’s ‘‘ Elements of Botany ”’.) 
consists of three parts, phloem, cambium and xylem. 
The phloem and xylem are exactly similar in nature to 
the phloem and xylem of the root, but the protoxylem 
and protophloem are found towards the centre, and not 
