9 
Vascular System of Pteris. 
(Figs. 1 and 2), corresponding with the union of the free margin a 
with the deep lateral hay of the leaf-trace below at z in Fig. 10. 
The contributions of the ventral limbs of the leaf-trace to the branch- 
steles in Pteris incisa var. integrifolia appears to have no parallel in 
Hypolepis. They are no doubt correlated with the much greater 
development of these ventral limbs in the Pteris. 
The strength of the foregoing comparison is increased by the 
fact that the leaf-trace of Pteris incisa (type, Fig. 4, c) is of exactly 
the same form as that of the two species of Hypolepis , but unfor¬ 
tunately no node of the former shewing the complication involved 
by branching of the stem is available for comparison. The petiolar 
strand of Pteris incisa (type) and of Hypolepis repens and tenui- 
folia shews a slight bay or concavity on each side, but this is not 
decurrent into the stele of the rhizome. In Pteris incisa var. inter:- 
rifolia on the other hand the petiolar strand is much more complex, 
and in correlation with this the solenostele of the rhizome does 
not become simple for some distance behind the node. The com¬ 
plication of the petiolar strand is mainly due to the much greater 
development of the two lateral bays (A 1 , B 1 in Figs. 9—12 and Fig. 3) 
and these are continued for some distance back in the rhizome, first 
as bays, then as hollow cylinders attached to the inside of the 
solenostele, and finally as open bays again (A and B in Figs. 6—8 
and Fig. 3), which eventually die out altogether. 
This increased complexity of the leaf-trace is no doubt a 
response to an increased demand for vascular tissue by an increased 
leaf-surface, and has resulted in an increased complexity of the 
vascular structure of the stem behind the node. 
Pteris aquilina. 
Let us now turn to Pteris aquilina. It is scarcely necessary to 
resume the vascular structure of the rhizome, the leading points of 
which have already been mentioned as described by Hofmeister and 
Stenzel, and are well-known to every elementary student. The 
connexion of the petiolar strands of the base of the petiole with 
those of the rhizome appears, however, never to have been 
accurately described. 
A transverse section of the base of the petiole, apart from the 
complications introduced by the arising of a lateral branch, shews 
an arrangement of the vascular strands easily derivable from the 
strongly curved plate which Gwynne-Vaughan has shewn to be the 
primitive type of leaf-trace in solenostelic ferns. In the dictyostelic 
