114 Sinnott.—Foliar Gaps in the Osmundaceae . 
leaf-bundle shows two well-marked gaps opposite the traces departing to 
the pinnae. 
In O. cinnamomea the very small vascular supply of the pinna leaves 
the foliar bundle in a curious fashion. The arch first bends outward near 
its ends, as in O. regalis. In this case, however, the trace, consisting of the 
xylem-arch with its included phloem and stelar parenchyma, is constricted 
off, and the gap behind it closed, before the xylem of the two bundles 
separates. Fig. 13 shows the condition of affairs before the gap has 
entirely disappeared. The trace to the pinna now breaks away from the 
leaf-bundle, and when seen at this height apparently causes no interruption 
in the xylem of the leaf-stele. The fundamental tissues on the inside and 
on the outside of the main bundle do not become continuous at this point 
as they do in O. regalis , a gap being formed in the xylem-ring only, just as 
in the stem, without breaking through the entire cylinder. This gap is an 
oblique perforation in the wall, and the interruption in the ring of wood can 
be seen at no one level. 
In O. Claytoniana the condition of affairs is somewhat more simple. 
The sides of the arch bend out as before, but in this case the trace breaks 
away quickly, and both its ends become free at about the same time. 
A gap is formed in the xylem only, the rest of the stelar tissue being merely 
constricted opposite the point of departure of the trace (Fig. 14). The 
xylem gap in this case is much longer than in the other two species, and 
does not close up for a considerable distance. 
In Todea barbara , the rachis is much stouter than in the filmy members 
of the genus, and the foliar bundle is consequently large. The trace of the 
pinna arises near the sides of the arch, as before, and, as in O. regalis , 
becomes free at its adaxial or lower end much sooner than at its upper one. 
Since the gap does not speedily close, however, the internal and external 
fundamental tissue become freely continuous through it. Fig. 15 shows the 
stage in the departure of the trace before it becomes entirely free. The 
break in the vascular tissue of the leaf-stele is not repaired till long after 
the separation of the pinna from the rachis. 
The leaves of the other three species of Todea are characterized by 
their so-called ‘filmy’ habit. The lamina is very thin, and possesses neither 
intercellular spaces nor stomata. The vascular supply to the leaf is 
consequently much reduced. 
In T. hymenophylloides the strand departing to the pinna leaves a well- 
marked gap in the leaf-stele through which the ‘ pith ’ and ‘ cortex ’ become 
continuous (Fig. 16). This gap, like the one in T. barbara , remains open 
for a considerable distance up the rachis. 
In the case of T . Frazeri , a clear break in the xylem is caused by the 
outgoing trace of the pinna, but the continuity of the vascular ring is not 
quite interrupted. A deep constriction occurs in it, however, along which 
