7 1 6 Gwynne- Vaughan . — Observations on the 
within the stele of D. repens at any point whatever. The 
xylem-ring is about ten times broader in the ventral region 
of the stele than it is in the dorsal, and the mass of enclosed 
phloem occupies in consequence a very excentric position 
(Fig. 33). The dorsal portion of the xylem-ring is very thin 
and forms a kind of bridge resting on the ventral mass, and 
arching over the enclosed phloem. The xylem-strand of the 
leaf-trace departs from this bridge, giving rise to a small gap, 
through which the internal phloem comes into contact with 
the external. The endodermis and pericycle which surround 
the external surface of the stele are not in the least decurrent 
through the leaf-gap ; they pass evenly across it, or at most 
only dip very slightly inwards. The leaf-gap closes up before 
even the xylem of the leaf-trace has yet separated off from 
that of the stem-stele. The structure of the internal phloem 
is quite normal, and the whole of it is probably to be regarded 
as metaphloem. The sieve-tubes nearest the bridge are some- 
what smaller than the rest, but no definite protophloem can 
be distinguished, nor does the external protophloem dip in 
through the gap in the xylem of the bridge. The leaf-trace 
departs as a single strand, more or less cordate or reniform in 
section. 
The steles of Davallia tenuifolia , Parkeri \ hymenophylloides 
and clavata were found to be precisely similar to that of 
D. repens , apart from slight differences in the relative thick- 
ness. of the ventral mass of xylem and the dorsal bridge, and 
in the amount of internal phloem present. The same type of 
stele is also to be found in fifteen or more different species of 
Lindsay a, but since a paper upon the anatomy of this genus 
is in preparation by Tansley no further reference need be 
made to them here. This type of vascular system has been 
called the Lindsay a-type by Tansley and Lulham, and since 
it is so characteristic of that genus it will be referred to in 
this paper by the same name. It should be noted, however, 
that there are at least two solenostelic species of Lindsay a. 
One of these, Lindsay a retusa , is perfectly typical and has 
already been mentioned. The solenostele of the other, 
