484 
Tans ley and Ltd ham. — A Study of the 
Another point is to be noted in connexion with the origin of this third 
leaf-trace. For a distance of -i mm., during the early stages of the separa- 
tion of the trace, the internal phloem of the stem-stele has a strongly curved 
form, into the concavity of which the xylem projects on one side of the 
base of the trace. This is the very simplest form of that £ local dilatation 
of the edge of the leaf-gap ’ which, as Gwynne-Vaughan has shown, forms 
the starting-point of the formation of internal accessory vascular strands. 
After the departure of the third leaf we have reached a point in this 
specimen so close to the apex of the stem that the whole of the tissue 
on the ventral side of the stele is in a meristematic condition, the xylem 
on the dorsal side of the central phloem being alone lignified. In the 
course of the next -i mm. the whole of this dorsal tissue of the stele, 
including the central phloem, is seen to be continuous with the fourth leaf- 
trace, while the ventral meristematic tissue ends in the stem-growing point. 
The actual growing apex is forced downwards by the early differentiation 
of the fourth leaf, so that it appears as a curved knob of meristematic tissue 
adhering to the ventral surface of the petiole. 
Plant B (Fig. 2) is very slightly more advanced than A. Its tissues 
were not very well preserved and present no new anatomical feature. The 
stele of the rhizome shows the same features as in the more advanced 
part of A, and the leaf-bundles are of corresponding type. 
Plant C, as may be seen from Fig. 3, possessed two leaves of con- 
siderably greater size and elaboration than those of A and B. A length of 
rhizome of a little over 1 mm. is preserved. The structure of the proximal 
end is essentially the same as the structure of B and that of the distal 
end of A, i. e. it consists of a hollow cylinder of xylem, with external phloem, 
pericycle, and endodermis, and enclosing a central strand of phloem which 
itself contains more or less connected endodermal cells. Passing forward 
towards the apex, the internal endodermal cells are continuous with a con- 
stant though irregular strand, consisting, on the transverse section, of 
several cells. The origin of the leaf-traces is, in this specimen, decidedly 
inconstant and irregular. Sometimes they are attached at right angles 
to the course of the stem-stele, while in other cases they pass off slowly, so 
that successive sections of the rhizome cut both stele and trace transversely. 
This form of variability is common in all the young plants. The cross 
sections of the different traces also vary considerably in form. The local 
dilatation of the xylem of the stele on one side of the attachment of the 
leaf-trace, already described in the case of the third trace of Plant A, occurs 
again in several of the traces of the present specimen. In one case the 
dilatation is continued forward as a ridge in front of the separation of 
the trace for a distance of -09 mm. ; it then becomes separated from the 
rest of the xylem of the stele and continues for -2 mm. as a free strand sur- 
rounded by the internal phloem. It becomes gradually thinner, but does 
