m PflYTOItOGIST. 
Vol. VI., No. 9 . 
Nov. 30 TH, 1907 . 
LECTURES ON THE EVOLUTION OP THE 
FILICINEAN VASCULAR SYSTEM . 1 
By A. G. Tansley, M.A. 
University Lecturer in Botany, Cambridge). 
LECTURE VII. 
Polycycly — continued. 
[Figs. 65—80.] 
In Pteris incisa var. integrifolia, and In Pteris aquilina we have 
a type of polycycly distinctly different from those we have 
hitherto been considering, for here the supply of part of the leaf- 
trace is the most important function of the internal accessory 
vascular system. 
Pteris incisa Thunb., according to Gwynne-Vaughan (’03), is a 
typical solenostelic fern, with a leaf-trace rather of the Hypolepis- 
type. In the variety integri folia there has been found 3 a curious 
complication probably connected with an increase in the elaboration 
of the frond. In the specimen examined (Figs. 65 and 66 ) each leaf 
arises in the angle between the two branches of a stem-dichotomy, 
the branches being so small relatively to the petiole that their steles 
arise by constriction from the sides of the leaf-trace, which forms 
the direct continuation of the vascular system of the main stem. 
The stele of the main stem (the diameter of which is about double 
that of Gwynne-Vaughan’s type) is a typical solenostele with a 
deeply waved outline. As the node is approached internal folds 
(Figs. 65 and 66 , A and B). arise from the inner wall of the vascular 
ring, one on each side of the stele. The whole structure increases 
greatly in size and the internal folds open to the cortex through the 
1 A Course of Advanced Lectures in Botany given for the 
University’ of London at University College in the Lent 
Term, 1907. 
* Tansley^ and Lulham (’04). 
