434 Bower.—Studies in the Phytogeny of the Filicales . 
conjunction with the leaves. Since Prof. Gwynne-Vaughan has concluded 
from the study of the lateral shoots of various Ferns that ‘ the ontogeny of 
the vascular system of the plant as a whole is very frequently repeated, 
although more or less imperfectly, in the development of the lateral shoots ’ 
(1. c., p. 724-5), this turns attention with special interest to the stolons 
of P. pycnophylla. 
The origin of the stolons appears to be always in connexion with the 
leaf-base, and from the adaxial side of it; but there is some variety in the 
proportionate size of the subtending leaf and of the stolon which it bears, 
and this presents an interesting morphological condition in certain cases. 
A simple example is seen in Fig. 10, where the subtending leaf has developed 
to a considerable size, and shows at its apex the circinate curvature ; it is in 
fact normal, but arrested in an early state. From its adaxial side has arisen 
the stolon, in this case a narrow one, with long internodes. In other cases, 
however, the stolon is larger in proportion, and the subtending leaf is smaller, 
being arrested in its growth at an earlier stage ; when this is extreme the 
appearance is as if the leaf-apex were substituted by a stolon, though in face 
of the former cases this cannot be accepted as the correct interpretation of 
them. The internal vascular structure accords well with these results 
of external observation. 
The attachment and basal structure of a relatively thin stolon is 
illustrated by the series of transverse sections in Fig. 11 (I—XIII), while they 
show also the relation of the stolon to the leaf, the adaxial face of which is 
constantly turned to the left in these drawings. In (I) the keeled leaf-base 
is shown traversed by a vascular strand which is, however, more contracted 
than it is usual for the leaf-trace to be ; this becomes crescentic higher up, 
with the horns directed abaxially (II), and thickens (III); soon a region 
differentiates in the centre of the xylem (IV), consisting of phloem, peri- 
cycle, endodermis, and sclerenchyma in succession inwards from the xylem, 
which has now opened into a complete ring ; except for the slight lateral 
horns the structure is very similar to that shown in the internode of 
Davallia aculeata by Gwynne-Vaughan ( 1 . c., PL XXXIV, Fig. 20); the 
strand has in fact widened into a solenostele, which still retains, however, 
the abaxial horns of the original foliar crescent. Presently the ring opens 
on the abaxial side (VI), and a part of the ring representing its abaxial 
region between the two horns abstricts first by one margin then by the 
other, and separating completely (VII, VIII) passes on as the vascular 
supply of the abortive leaf-apex. The solenostele very shortly closes the 
gap (IX, X), the point of closure remaining obvious for some time as 
a thinner region; the ring soon opens again, but now on the adaxial side 
(XI), to give off the vascular supply of the first scale-leaf of the stolon 
(XII, XIII). 
An example of a typically solenostelic structure is seen in Text-fig. 4, 
