225 
The Anatomy of Dioon edule, Lindl. 
present (Fig. 36, b). The internal peduncular dome gives off in 
two irregular whorls a number of leaf-traces similar in origin and 
character to those from the cauline cylinder; these pass radially 
outwards through the main cylinder into the cortex, where they 
behave like the ordinary girdle-bundles (Fig. 36, l.t. II.) 
This peculiar arrangement of the vascular tissues is clearly a 
result of the sympodial growth of the stem (see Figs. 37 and 38). 
The cone terminates the main axis, the dome-shaped vascular 
system being the normal condition at the stem apex. The main 
I 
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Fig. 37. Diagram representing the relation of the vascular system of the chief 
lateral bud to that of the primary axis and peduncle. ax. cyl., the 
main axial cylinder narrowing into ped. cyl., the peduncular cylinder; 
bud. cyl., cylinder of the lateral bud which continues the growth of 
the trunk. 
growth of the stem is continued by one of a pair of opposite lateral 
buds, the vascular tissue of which unites with that of the main axis 
in a horizontal ring; the upper surface of the vascular dome of 
the bud having a gap through which the peduncular cylinder, 
passes. Later, as the lateral bud becomes terminal by the in¬ 
creased growth of the under side, the peduncular cylinder, 
persisting after the cone has fallen, is thrust over to the side 
remote from that on which the bud originated; so that it even 
comes to slope downwards in the cortex. The vascular cylinder 
of the lateral bud increases greatly in size, and eventually appears 
continuous with the original cauline cylinder; the true apical dome 
remaining enclosed in what is now the main conducting cylinder of 
the trunk. 
The aborted bud (Fig. 36, b) beneath the peduncle is the 
second lateral branch of the primitive dichasium, only one branch 
of which developes. 
Figures 35 and 36 represent semi-diagramatically dissections 
of two pieces of the trunk in the region where the internal cylinder 
