MORPHOLOGY 
netti tales are lateral, but distributed along the stem; while in Cycadales 
they are lateral, but restricted to the tip of the stem. 
Vascular anatomy. The anatomy of the stem resembles that of the 
Bennettitales, with a thick cortex, a thin vascular cylinder, and a large 
pith (fig. 438). The 
vascular bundles of 
the stem are collateral 
and endarch, as usual 
among gymnosperms; 
but in leaf traces, or 
leaf veins, or axes of 
strobili, the old fern 
connection is indi- 
cated by mesarch 
bundles and some- 
times even by con- 
centric bundles. It 
is in these so-called 
peripheral regions of 
the body that the 
older features of the 
vascular structure 
persist the longest. 
The primary cambi- 
um of the stem may 
persist (as in Zamia), 
although the amount 
of secondary wood it 
forms is always small; 
or it may be of short 
duration (as in Cycas), 
in which case a series 
of successive cambium 
cylinders is formed in 
the cortex, resulting 
in a concentric series of vascular cylinders. The leaf traces differ 
very much from those of the Bennettitales. Instead of being direct, 
as in the latter group, some of them (usually two) pass around the 
stem through the cortex, and often enter a leaf on the opposite side of 
FIG. 435. Bowenia (oriental), showing tuberous stem 
with heavy armor of leaf bases. After EICHLER (ENGLER 
and PRANTL). 
