1 88 Gibson. — Contributions towards a Knowledge 
stele of that side on which the branch arises splits into two steles, 
one carrying the traces of the dorsal leaves of that side, the 
other carrying the traces of the ventral leaves of the same side. 
A similar splitting takes place in the other stele on the side 
away from the origin of the branch. There are thus differen- 
tiated, above the origin of the youngest branch, the four steles 
which form the basis of the vascular system. The steles are 
generally connected in pairs by their pericycles, or at least 
occupy a common lacuna. When the branch fuses with the 
more vigorous axis, the stele of the branch which lies next to 
the chief axis fuses with the dorsal stele of the pair on that 
side, whilst the outer stele of the branch fuses with the ventral 
stele of the main axis of the same side, which latter receives 
also the leaf-trace of the axillary leaf. The two conjoint steles 
now pass downwards but fuse, at least so far as their pericycles 
are concerned ; so that a section of a slightly older axis may 
show only two steles laterally placed ; or three, where the right 
or the left pair may be connected by their pericycles; or four, 
when all are distinct as in more mature branches. 
2. Anatomy of the primary erect shoot . 
The unbranched portion of the erect shoot shows in 
section eleven, twelve or even thirteen steles, though two or 
more of these may be united by their pericycles. The 
accessory steles are separated off from the four primary steles 
(i. e. from those which carry the leaf-traces), apparently with- 
out any very definite order ; for after examining several shoots 
I found so much variation in the branching of the accessory 
steles, that I felt that the number and order of these could 
not be a point of fundamental importance. 
If the vascular system of an erect shoot, still unbranched, 
be traced from the apex down to the creeping rhizome, it will 
be found that quite at the apex the four primary steles are 
clearly distinguishable in procambial form — and alone receive 
the leaf-traces ; within are to be seen (in a definite instance) 
seven accessory steles, one of them double. These accessory 
steles do not carry leaf-traces, but separate away from, or 
rather anastomose with the four primary steles lower down. 
