92 G wynne- Vaughan. — Observations on the 
they are of too speculative a nature to compete with the more 
pronounced relationship between it and the Dennstaedtiinae. 
To begin with the Gleicheniaceae. No case of simple 
solenostely is known in this family, the nearest approach 
among allied groups being the highly complex and remarkable 
vascular arrangement recently described by Seward (1. c.) in 
Matonia pectinata , R. Bi\. the explanation of which I am 
inclined to seek in the profound modification of some more 
simple solenostelic ancestor. It is interesting to discover 
that the form of the petiolar meristele of Matonia is a slight 
modification of the horseshoe, as indeed is also the case in 
Gleichenia itself, where the arms of the horseshoe are curved 
inwards to such an extent that they meet together in the 
median line, thus enclosing a small mass of sclerenchymatous 
ground tissue in the centre of the horseshoe. However, at 
one level or another in the petiole of Gleichenia dichotoma , 
generally near the base, I have found that the arms of the 
horseshoe separate from one another so that the enclosed 
ground-tissue becomes continuous with that outside the 
meristele ; thus the hippocrepiform nature of the meristele 
becomes quite clear. It should be mentioned that both 
sclerosed sieve-tubes and cavity-parenchyma are to be found 
in G. dichotoma. 
As regards the Hymenophyllaceae , the universal occurrence 
in the stem of a solid central cylinder clearly places them 
anatomically much farther away from Loxsoma than are the 
Cyatheaceae, and this estrangement is deepened by the 
plentiful display of stomata and intercellular spaces in 
the lamina of the leaf of Loxsoma , which are never to be 
found in the Hymenophyllaceae , not even when the lamina 
is several layers thick, as in Trichomanes reniforme . For 
all that, there are several points that suggest a certain 
relationship, although it may be a somewhat distant one. 
It is especially in the vascular strand of the petiole that these 
points are to be sought ; for, although the outline of the 
vascular strand as a whole is, in most of the stouter species, 
oval or roughly triangular, yet I believe it possible to 
