*7 
Anatomy of the Ophioglossaceae. III. 
supply to the branch can be followed from Text-fig. 4. The first section (a) 
shows the preceding leaf-gap still open and the position of the vestigial bud 
above it. On the other side of the median line the protoxylem of the next 
leaf-trace is recognizable, separated by inner xylem from the pith. In 
B the condition is similar, but the section now passes through the canal 
leading to the vestigial bud, and the gap in the xylem is narrowing. In C 
the canal has almost reached the surface of the rhizome, and the leaf-gap 
is closed, although the external xylem is not of full thickness across it. 
On the other side of the middle line, the nascent leaf-trace is more evident, 
and the inner xylem has largely disappeared opposite its protoxylem. 
To either side of the xylem of the trace, which still forms part of the 
complete stelar ring, the first indication of the vascular supply to the branch 
is visible. At these points an additional development of tracheides has 
taken place immediately outside those of the normal xylem. This xylem, 
which is indicated in the figures by cross-hatched shading, corresponds in 
a sense to secondary xylem, and will be referred to as accessory xylem . 
In the next section (d) these patches of accessory xylem are much larger, 
and the new development extends further round the stele, though confined 
to its upper side. The leaf-trace is seen to be purely endarch as it departs, 
and the inner xylem is wanting opposite to it. The separation of the 
trace is further advanced in E ; this shows a new feature, in that the inner 
xylem, which at the preceding level was well marked to either side of the 
nascent leaf-gap, now extends across below the gap, and also out into it. 
This inner xylem, together with the accessory xylem evident to either side 
of the leaf-gap, is destined to supply the stele of the branch subtended by 
the departing leaf-trace. The actual appearance of the stele about this 
level is shown in PL II, Photo 22, in which the tracheides of the accessory 
xylem (x. 2 ), and those of the inner xylem filling up the gap (x.i.) will be seen 
to have stained more faintly than those composing the normal primary 
xylem of stele and leaf-trace. The next sections in Text-fig. 4 show how 
the xylem of the branch stele becomes constituted. At the level of Text- 
fig. 4, F, the leaf-trace was departing from the cortex. The endodermis has 
become completed over the leaf-gap, and the inner xylem has passed 
outwards through the gap, and come into contact with the two groups of 
accessory outer xylem that have extended towards the middle line of the 
gap. The actual appearance about this level is shown in PI. II, Photo 23. 
In G, the two groups of accessory xylem have joined to form an arc of 
xylem, against the inner face of which lies the group of inner xylem. 
The xylem of this nascent branch-stele is now distinctly separated by 
parenchyma from the main stele, the gap in the xylem of which is seen to 
be still open. The outer xylem of the branch stele now becomes continued 
around the inner xylem, between the elements of which parenchyma has 
appeared. This process, begun in Text-fig. 4, H, is complete in I, although 
c 
