Sahni . — On an Australian Specimen of Clepsydropsis . 89 
relative positions and shapes of the different parts of the xylem, and in 
a few cases (Text-fig. 2) they have even broken the latter into two or more 
pieces. 
One of the leaves shows further branching of the vascular supply 
(Text-fig. 2, 2 ). In this case a small elliptical ring of xylem is seen lying 
just off the pinna-trace, adaxially to it, at an angle of 45 0 . Owing to 
bad preservation, in the only other section that passes through this leaf 
there is no sign of this strand, so that it is at present impossible to ascertain 
its point of origin, whether from the pinna-trace or directly from the 
primary leaf-strand ; but from the direction of the long axis of the ellipse 
(due to oblique section of a circular tube) it seems highly probable that it 
arose from the pinna-trace. In view of the proximity of intruded roots, 
however, it is quite likely that the strand in question has been shifted slightly 
out of its natural position. The obliquely-cut tracheides show a finely 
scalariform pitting ; no spiral or annular elements are seen. The thickness 
of the ring is about three tracheides ; the tissue in the centre of the ring is. 
not preserved. 
V. Theoretical. 
Aphlebiae . In C. antiqua Dr. Bertrand (1911 a, pp. 15-17) has 
figured a small ring-like strand occupying a rather similar position. This 
strand evidently has the same morphological value in both cases. Dr. 
Bertrand regards it as the trace of a pinnule (tertiary rachis). It is probable, 
as Professor Seward suggested, that the organs supplied by these tertiary 
strands were of the nature of aphlebiae. This supposition is confirmed by 
a comparison with the corresponding structures in Diplolabis Roemeri , 
Metaclepsydropsis duplex (Gordon, 1911 a , b), Stauropteris oldhamia 
(Bertrand, 1909, p. 29, Fig. 4). The strands referred to by Stenzel (1889, 
p. 45) as arising from the base of the leaf-trace are also probably of the 
same nature. 
Better preserved material is necessary to decide the question as to the 
normal number and position of the aphlebia-strands on each side of the 
pinna in Clepsydropsis (Unger, 1856, p. 167 ; Solms, 1896, pp. 25-7 ; Stenzel, 
1889, pp. 21, 23) ; a re-examination of Stenzel’s original specimens of 
C. kirgisica would be useful. 
Habit. — The known genera of Zygopterideae may be classified into two 
groups, the Clepsydroideae (including the genera Asterochlaena and Clepsy- 
dropsis) and the Dineuroideae (including Dineuron , Diplolabis , Metaclepsy- 
dropsis , Etapteris , Stauropteris , Zygopteris , and provisionally Gyropteris 
sinuosa , which may ultimately have to be placed as a species of either 
Diplolabis or Metaclepsydropsis ). Except for Gyropteris , these two groups 
are co-extensive with those proposed by Kidston and Gwynne-Vaughan 
(1910, p, 470) on the basis of the number of (free) branch-axes on each side 
