722 Boodle . — ■ Anatomy of the Gleicheniaceae . 
phloem-band splits, and pass into the stelar part of the nodal 
island, but die out upwards almost at once, i. e. at the level of 
the first appearance of the xylem-bridge. 
In a third node, when the leaf-trace separates, its xylem is 
closed, as in the previous cases, but becomes open while the 
leaf-trace is still in the cortex of the stem. 
In the fourth node examined, the bar of xylem which 
usually appears in the nodal island, cutting it into two, is 
not formed, and the leaf-trace consequently passes off from 
the stele with an open xylem-arch, leaving the inner part 
of the original nodal island as simply a bay in the exterior 
of the xylem. In this case the phloem in the nodal island 
and the internal phloem of the leaf-trace both have a con- 
nexion with the external phloem of the stele, though this was 
of course not the case in the other three nodes. 
In the last two nodes mentioned, the leaf-trace passes off in 
the median plane of the stele, i. e. from a point on the opposite 
side from the lower median lobe, not obliquely as in Fig. 18. 
It is no doubt in connexion with this that the behaviour of the 
protoxylems is much simpler than in the first node described. 
In the last two nodes, the upper median protoxylem of the 
internode passes out as the median protoxylem of the leaf- 
trace, whose two lateral protoxylem-groups are supplied by 
forking of the two upper lateral protoxylems of the internode. 
Thus the behaviour of the protoxylems and the position of 
the leaf-trace as it leaves the stele show that the leaf- 
arrangement should be regarded as tristichous, median and 
slightly lateral leaf-traces being produced. 
The petiole, belonging to the second node described, was 
14! cm. in length, and was sectioned at close intervals. The 
results need not be given in detail, but one or two changes in 
structure should be referred to. The central sclerotic mass 
with its investment of endodermis divides into three, and then 
fuses again (as in Figs. 9 and 8). It appears to remain per- 
manently enclosed in the bundle, having no connexion with 
the cortex or the outer endodermis. The xylem of the bundle 
in this petiole remains closed until a height of 4-5 cm. is 
