in the ‘ Seedlings' of Certain Leptosporangiate Ferns . 377 
A root-trace then joins the cauline system approximately opposite the 
previous leaf, but hardly is its connexion complete when the vascular ring 
opens, and from each of the two horns thus formed a strand is constricted 
off to form a double leaf-trace, a condition hinted at in the bilobed appear- 
ance of the xylem of the first leaf-trace. The two leaf-bundles pursue 
a curved course through the cortex, leaving the cauline system almost 
horizontally. During their exit, a group of endodermal cells appears 
in the internal phloem between the xylem arc and the outgoing trace, 
and at a slightly higher level an endodermal ring surrounds a group of 
large parenchyma cells closely resembling the fundamental-tissue. At the 
leaf-gap, this inner endodermis joins up with the external sheath, which, 
owing to the horizontal and band-like leaf bundles, presents at this level 
the somewhat peculiar appearance represented in Figs. 152-J 54. We thus 
have in this plant, as in Lomaria Spicant , a pocket of fundamental-tissue 
laid down in the region of the leaf-gap, and shut off from the vascular 
system by an endodermis. 
After the completion of the trace, the two strands of which quickly 
unite to form a single petiolar bundle, the cauline strand has the form 
of a curved band, which receives a root-trace opposite the last leaf. The 
xylem then immediately breaks into two strands, the previous leaf-gap 
remaining open. The whole cauline strand, however, is still surrounded by 
a common endodermis (Figs. 156, 157). 
The next leaf-trace is double, and formed from the horns guarding the 
new break in the xylem by a process of simple constriction. There is 
no pocket of fundamental-tissue formed in connexion with this leaf-trace, 
whose extreme simplicity of origin is somewhat masked by the difference 
in levels at which the two components leave the cauline system, and 
by their horizontal course through the cortex. As before, the final trace is 
single, but its double origin is obvious (Figs. 158, 159). 
After the exit of the trace, the ground-tissue gradually separates 
the two vascular arcs, each of which finally possesses its own endodermal 
sheath, as in Figs. 159 and 160. One of the vascular arcs receives 
a root-trace, and, before its junction with the latter is really complete, 
divides into two parts ; a fusion of one part with the remaining original 
cauline vascular strand occurs, and a leaf-trace is formed by the nipping 
off of two strands exactly as before (Figs. 162-164). The whole process is 
then repeated again and again, the double leaf-strands remaining separate 
for increasingly longer periods, fusion finally occurring in the base of the 
petiole. 
In connexion with the later- formed leaf-traces, it was found that 
the division of the cauline strand commences just before the entry of the 
corresponding root-trace, and consequently the latter has a double inser- 
tion upon the cauline system. The later roots, too, have a somewhat 
D d 
