196 STEMS 
The vascular bundles of all Dicotyledons are very sim- 
ilar to those of Monocotyledons in structure and function 
of conductive vessels, but differ essentially in having cambium. 
(Fig. 174.) The conductive tissue of the xylem consists 
chiefly of annular, spiral, pitted, and scalariform vessels — the 
latter being so named because the thickened areas, separated 
by slit-like thin areas, are so arranged, one above another, as 
to resemble the rounds of a ladder. Asin Monocotyledons, the 
xylem vessels, probably assisted by the neighboring parenchyma 
cells, are the passage ways through which the water and 
dissolved substances absorbed by the roots are distributed 
throughout the shoot. In addition to sieve tubes and companion 
WS. a 
RRQ 
SSG 
SINS We: 
i # ¢bYy b 
Fic. 175. — Cross section of a Flax stem. a, epidermis; d, bast fibers; 
c, cambium; p, phloem; xz, xylem, A, pith. Enlarged. 
cells, the phloem of Dicotyledons generally contains many thin- 
walled parenchyma cells, which serve in conducting the carbohy- 
drates and also as storage places for proteins. The sieve tubes 
and companion cells conduct the proteins and a part of the carbo- 
hydrates. The bast fibers, which commonly occur in connection 
with the phloem of all Dicotyledons, are tough flexible strands 
adapted to afford strength. In fiber plants, such as Flax and 
Hemp, the bast fibers are well developed and their importance 
in the manufacture of fabrics, as the manufacture of linen from 
Flax, is well known. (Fig. 175.) 
In contrast to the stems of Monocotyledons, the stems of Di- 
cotyledons and Gymnosperms have as their distinctive features 
the circular arrangement of vascular bundles and the presence 
