Bower.—Studies in the Phytogeny of the Filicales. VII. 37 
abaxial part of the trace, which now forms a closed ring (Fig. 2 6 , b). 
The behaviour of these vascular tracts in supplying the first pinnae and the 
extension of the rachis is shown in Fig. 26, c-i. Extending laterally 
the ring flattens, and two processes are formed on either of its flattened 
sides (c). These approach and meet, resolving the ring into three loops. 
Meanwhile similar fusions right and left of these re-establish connexion 
between the adaxial and abaxial tracts ( d , e,f). Splittings which follow 
these fusions result in the establishment of three separate traces, supplying 
respectively the two pinnae and the continuation of the rachis. The former 
(g, i ) have each a connected, but slightly unsymmetrical horseshoe; the 
latter repeats on a smaller scale the structure of the petiole ( h ). What has 
been described was seen in an individual 
case, and it is not known whether the 
relations are constant in leaves of 
large size in this species. Nothing 
exactly like this has been seen in other 
Ferns. There is, however, some distant 
resemblance to what has been described 
for large leaves of Lophosoria and 
Gleichenia ; and analogous cases will 
probably be found in other large-leaved 
Ferns. 1 The nearest analogy, however, 
is with the condition of the petiole of 
AcrOstiehum aureum , L., as described 
by Frau Schumann. 2 
Pteris podophylla shows an extra¬ 
ordinary complexity of the vascular 
structure of its stem in large plants. 
It has already been noted by Mettenius, 
evidently in plants of medium size, for 
he compares it with what is seen in 
Pteris elata? The material collected in Jamaica has served for tracing 
the development from the beginning to the fully adult state. Several 
young plants were cut serially, and parts of older plants, and from 
them the following account has been constructed, which shows that a much 
more complicated state is attained than in P. elata. 
At the base is a protostele with parenchyma scattered among the 
tracheides. The parenchyma increases centrally to form a pith. At 
a comparatively early stage, and before phloem is present in quantity, this 
is converted into a solenostele by the process described as ‘ pocketing ’. 
This structure is continued for several internodes in the usual way. But 
1 Compare Studies, II, PI. XXXV, Figs. 14, 15. 2 Flora, 1915, p. 212, Figs. 6, 7. 
3 1 . c., p. 535 - 
Fig. 26. a, b. Transverse sections of 
the petiole of Pteris (Litobrochia) podophylla ; 
c-f show the steps of change to form the two 
first pinnae; g-i show 7 the stalks of those 
pinnae, and of the rachis. Natural size. 
