712 Gwynne- Vaughan. — Observations on the 
differences. Thus in Alsophila excelsa the internal strands of 
one leaf-gap are not related to any of the other leaf-gaps, nor 
are the internal strands of succeeding leaf-gaps in any way 
joined up or connected with one another. It should also be 
noted that in this plant the internal strands do not appear at 
all until the ordinary stelar cylinder has become more or 
less dictyostelic. 
The real nature of the accessory cortical strands that occur 
in certain Cyatheaceae ( Cyathea arbor e a, Alsophila armata , 
&c.) is not as yet known with certainty. Two concentric 
rings of vascular strands are also present in the stems of 
Acrosticum scandens and A. tenuifolium (. Lomaria fraxini - 
folia). According to Bertrand and Cornaille 1 the leaf-traces 
arise from both of these two rings, but which of the two is 
to be regarded as the typical stelar cylinder has not yet been 
decided. 
In the stem of Davallia immersa , again, two concentric 
series of vascular strands are present. The central ring alone 
gives off the leaf-traces, and probably represents the typical 
stelar cylinder. My material was not sufficient to determine 
the nature of the small peripheral strands. It is possible, 
however, that they are merely root-steles that run forwards 
for a long distance in the ground-tissue of the stem before 
turning outwards. 
Davallia aculeata and D. pinnata. 
The stem of Davallia aculeata , like those of the other 
solenostelic Davallias, is a dorsiventral rhizome with the leaves 
inserted in two rows upon the upper surface, but the soleno- 
stele itself differs so much in structure from those already 
described that it deserves especial mention. Instead of sur- 
rounding a central mass of ground-tissue as a hollow vascular 
cylinder, the wall of which is of the same breadth throughout 
as in the previous examples, the ventral region of the soleno- 
1 Jitude sur quelques caracteristiques de la structure des Filicides actuelles. 
Memoires de l’Universitd de Lille, tom. x, no. 29, p. 136, 1902. 
