CHAPTER XXV 
MONOCOTYLEDONS AND DICOTYLEDONS 
249. Contrasting characters. The two great groups of 
Angiosperms are quite distinct, and there is usually no dif- 
ficulty in recognizing them. The monocotyledons are 
usually regarded as the older and the simpler forms, and 
are represented by about twenty thousand species. The 
Dicotyledons are much more abundant and diversified, con- 
taining about eighty thousand species, and form the domi- 
nant vegetation almost everywhere. 
The chief contrasting characters 
may be stated as follows : 
Monocotyledons. (1) Embryo 
with terminal cotyledon and lat- 
eral stem-tip. This character is 
practically without exception. 
(2) Vascular bundles of stem 
scattered (Fig. 332). This means 
that there is no annual increase in 
the diameter of the woody stems, 
and no extensive branching, but 
to this there are some exceptions. 
(3) Leaf veins forming a closed 
system (Fig. 333, figure to left). 
As a rule there is an evident set 
of veins which run approximately parallel, and intricately 
branching between them is a system of minute veinlets not 
readily seen. The vein system does not end freely in the 
376 
FIG. 332. Section of stem of 
corn, showing the scattered 
bundles, indicated by black 
dots in cross-section, and by 
lines in longitudinal section. 
From "Plant Relations." 
