Bower.—Studies in the Phytogeny of the Fi lie ales. 429 
branches again unite at the upper limit of the swelling into a single strand, 
and in this form it passes up through the whole length of the leaf. The 
only statement I know as to the structure of the stock is by Gwynne- 
Vaughan; 1 he figures a transverse section of a rather small stock ( 1 . c., 
Fig. io), with the remark (l.c., p. 697) that it is radially dictyostelic, but 
still remains very close to solenostely. 
A transverse section of a large stock of P. pycnophylla accords entirely 
with this description (Fig. 6) ; it appears very irregular in outline as 
a consequence of the closely aggregated leaves with their decurrent 
insertion. Their arrangement is on a complex spiral, which varies with 
the size of the stock. Each is plainly served by a single V-shaped vascular 
strand, which is accompanied on its way by a broad flanking sheet of dark 
sclerenchyma on its outer side, and a small patch of the same in the fork 
of the V. Each leaf-base is subtended on its adaxial side by a deep 
involution of the surface, of semilunar outline convex inwards, and lined by 
sclerotic tissue. It will be observed, by comparison of the leaf-traces 
in the section figured, that internally, opposite each leaf-trace at its first 
separation from the axial stelar ring, there is a patch of sclerenchyma ; 
as the leaf-trace passes outwards this sclerenchyma expands, taking 
gradually the semilunar form ; it is in the middle of these patches that the 
involutions make their appearance, widening out (as seen in the transverse 
section) till the leaf-base which each subtends is completely separated from 
the stock. A similar involution has been noted in other Ferns, and among 
the Helicogyrate types which show it are Anemia and Onoclea ? 1 
The middle of the massive axis is occupied by a column of pith, 
the central region of which is sclerotic, while isolated smaller strands of 
sclerenchyma about its periphery mark the position where the successive 
foliar gaps will be formed by passage outwards of the leaf-traces. Sur¬ 
rounding the pith is an almost complete solenostele, interrupted only here 
and there by the separation of the foliar traces from it: these appear first 
as outwardly projecting bays opposite to the sclerotic strands already men¬ 
tioned, and finally they break away from the solenostele by abstriction right 
and left. The roots, which are seen in large numbers traversing the cortex, 
spring as a rule from the margins of the gaps thus left by the outgoing traces. 
The stelar ring is delimited internally and externally by a brown 
coloured endodermis, which is continuous through the foliar gaps, and is 
lined internally by a pericycle of 1-3 layers. The phloem is abundant both 
1 Solenostelic Ferns, II. Ann. Bot., xvii (1903), p. 689. Gwynne-Vaughan names the plant on 
which he worked Plagiogyria biserrata (= Lomaria semicordata) ; but as his material came from 
the Eastern tropics this cannot be correct; there are no herbarium specimens of the same collection, 
so it is impossible to check the determination ; but all the characters point to the plant having been 
P. pycnophylla. 
2 Compare Gwynne-Vaughan : On the possible existence of a Fern stem having the form of 
a lattice-work tube. New Phyt., iv, p. 211. 
