6g8> Gwynne- Vaughan.— Observations on the 
pellucida , Taenitis blechnoides , Gy 7 nnogramme calomelanos 
(Fig. 9), Hemionitis palmata, Adiantum lunulatum , Lomaria 
semicordata (Plagiogyria bis errata, Met.) (Fig. 10). No 
particular form of leaf-trace is especially related to the 
simpler intermediate forms of dictyostely, either dorsiventral 
or radial. However, it generally consists of a single strand, 
as in Nothochlaena Marantae (Fig. 7) and Pteris tremula , 
or else it is divided into two separate portions, as in Adiantum 
trapeziforme and Gymnogramme calomelanos (Fig. 9). 
Whenever more than two rows of leaves are found upon 
the stem of a Fern they are nearly always arranged radially 
all round the axis, even though it may be a creeping or pros- 
trate rhizome. There are, however, a few in which they 
are inserted in several rows all upon the upper surface, and 
in these the rhizome is dorsiventral in structure, e. g. Pellaea 
cordata. It seems probable that they originally belonged 
to the radial type, and have become dorsiventral in a 
secondary manner in consequence of the prostration of the 
stem. It is also possible that they have been derived from a 
dorsiventral type with two rows of leaves by the intercalation 
of additional leaves between those already present. However, 
their anatomy has not yet been thoroughly investigated, 
and the question must be left open. 
SOLENOSTELES WITH INTERNAL ACCESSORY VASCULAR 
Strands. 
Attention has already been drawn to the fact that the 
free margin of the leaf-gap in Dickso 7 iia apiifolia and other 
solenostelic Ferns is considerably thicker than the rest of the 
solenostele, owing to an increase in the amount of xylem 
present at that point. In Dicksonia adiantoides this feature 
becomes so conspicuous and important that it requires especial 
description ; particularly so because it appears to give an 
explanation of certain complex modifications of the vascular 
system that occur in a number of other Ferns. Dickso 7 iia 
adiantoides has a dorsiventral rhizome with leaves in two 
rows on the upper surface, and a perfectly solenostelic vas- 
