98 PRACTICAL COURSE IN BOTANY 
and back from the leaves to the parts where it is needed after 
it has contributed to the elaboration of food. 
On account of this double line of communication which 
they have to maintain, the vascular threads, or bundles, as 
they are technically called, are double; one part composed 
of larger vessels, carrying water up, the other consisting of 
smaller ones, bringing back the food. Can you give a reason 
for their difference in size? 
112. Woody monocotyls. — Examine sections of yucca, 
smilax, or of palmetto from the handle of a fan, and compare 
them with your sketches of the cornstalk. 
In which are the vascular fibers most abun- 
dant? Which is the toughest and strongest? 
Why? Trace the course of the leaf fibers 
from the point of insertion to the interior. 
How does it differ from that of the fibers 
in a cornstalk? 
113. Growth of monocotyl stems. — After 
tracing the course of the leaf veins at the 
nodes of the cornstalk, you will have no 
difficulty in identifying these veins as part of 
the vascular system. In jointed stems like 
_ Fr L those of the corn and sugar cane and other 
rh : W vaenrs grasses, their intercalation between the vas- 
of a palm, showing eylar bundles of the stem takes place, as we 
the curved course of , 
the fibrovascular have seen, at the nodes, forming the hard 
ete Bett afer rings known as joints; but in other mono- 
cotyls the fibers entering the stem from the 
leaves usually tend first downward, toward the interior 
(Fig. 114), then bend outward, toward the surface, where they 
become entwined with others and form the tough, inseparable 
cortex that gives to palmetto and bamboo stems their great 
strength. Generally, monocotyl stems do not increase in di- 
ameter after a certain point, and as they can contain only a 
limited number of vascular fibers, they are incapable of sup- 
porting an extended system of leaves and branches. Hence 
