DICKSONIEAE 591 
runs round two sides, but at the point (*) it appears to stop, but it does not 
do so actually: it merely curves round upon the peripheral face, and dis- 
appears behind the body of the sporangium. That the annulus is really 
a continuous one is seen from Fig. 3298, which represents the peripheral 
face: it is very irregular, especially at the base of the sporangium, and 
consists of a large but not definite number of rather narrow cells; together 
they form a twisted hoop, so disposed that the distal end of the hoop is 
curved in the direction of the apex of the receptacle, and this curvature 
makes the sporangium a peculiarly difficult object to represent in a drawing. 
The thickening of ‘the walls is greater at the distal part of the annulus than 
at the proximal, while at one side or the other is a part not strictly defined, 
where rupture will take place. There is no definite stomium, and though 
rupture usually occurs about the region to the right in Fig. 329 , the 
actual point of dehiscence may vary. 
The features thus noted mark off the annulus of Zhyrsopteris as one of 
the least specialised among Leptosporangiate Ferns: the inequality of its 
thickening suggests a comparison with Zoxsoma. It seems probable that, 
while showing clear points for comparison with Dicksonia, it has been derived 
from a type with a completely indurated annulus and median rupture: that 
this became modified in consequence of the close packing of the sporangia 
in the sorus, which would interfere with a median dehiscence: that a lateral 
rupture had been adopted, but the sporangium not definitely specialised for it. 
The anatomy of Zhyrsopéeris is very imperfectly known. The leaf shows 
a vascular system, with a few separate bands arranged in the usual horse- 
shoe outline ; in fact, the structure suggests similarity with Dicksonza. There 
are no data as to the internal structure of the axis. 
From the known characters it would appear that the relationship of 
Thyrsopteris is primarily with Dzcksonia, but in some remote degree also 
with the Hymenophyllaceae: there appears little reason to relate it to the 
Cyatheaceae, as has been suggested by various writers. It is, however, 
best placed as a separate family, on account of the peculiar characters of 
the sporangium and annulus: these show less perfect differentiation than 
of the Ferns named, while an archaic character is indicated by the numerous 
cells of the annulus, and the imperfect localisation of the point of 
rupture. 
DICKSONIEAE. 
The family of the Dicksonieae included, as arranged in Hooker's Synopsis 
Filicum, six genera; but of these the affinity of Oxoclea appears to be rather 
with the Cyatheae, while Hy,oderris, Woodsia, Sphaeropteris, and Deparia 
differ from Dicksonéa itself not only in the position of the sori, which are 
superficial (except in Deparia}), but also in the fact that the various ages 
1 Deparia Moore’, a fern in which the sori are mostly marginal, shows occasional 
superficial sori also: but these are upon the upper surface, and the case is perhaps com- 
parable with that of Aspidium anomalum. Hk. and Arn: see p. 117. 
