124 Vascular Strands of Fern-Seedlings. 
In the first type, represented by Doodia aspera, we find the 
ground tissue at the leaf-gaps replacing the vascular tissue to 
such an extent as to divide the latter into two strands, an elemen¬ 
tary dictyostelic structure thus being arrived at immediately. 
In the second and more common type we find in connection 
with the fifth, sixth or seventh leaf-trace, the appearance of what 
the writer proposes to term a “ground-tissue pocket,” closely 
resembling the “ endodermal pockets ” described by Boodle ; the 
writer believes, however, that the former term more correctly 
indicates the essential nature of the phenomenon. 
The vascular system at the region of such a ground tissue- 
pocket presents in all essentials the siphonostelic structure regarded 
by Jeffrey'as primitive, but there seems to be no good reason for 
ascribing such preponderating significance to an arrangement of vas¬ 
cular tissue, such as, in all probability, is merely the expression of the 
most efficient mechanical distribution of the tissues concerned. 
The ground-tissue pockets are generally very shallow, the external 
and internal portions of the ground-tissue becoming continuous at 
the leaf-gap which occurs at an immediately higher level. Quite 
exceptionally however, it happens that the pocket may persist 
through some little distance, and the occurrence of such an internal 
differentiation of ground-tissue may possibly afford a simple expla¬ 
nation of the highly interesting structure occurring in Osmunda 
cinnamotnea as described by Pauli. 
Polypodium aureum proved to be an extremely interesting 
plant. Leclerc du Sablon, examining the transitional region of 
very young plants, describes the occurrence of a central strand of 
parenchyma in the solid rod of xylem. This has been denied by 
Jeffrey, and the present work fully confirms the statements of the 
latter writer. The interest of the plant, however, lies in the fact 
that after the first two or three leaf-traces (which are formed in a 
very simple manner), the cauline strand divides directly into two, 
affording almost a demonstration of the condition of affairs assumed 
by Van Tieghem as an explanation of his polystelic type. It will 
be remembered that Miss Ford has described a similar state of 
things in Ceratopteris thalictroides, but the writer hopes to be able 
to show that the vascular system of Polypodium aureum at any rate 
is essentially phyllosiphonic in character, its true nature being 
rendered obscure by the occurrence of double, and later, multiple 
leaf-traces, in conjunction with internodes of somewhat unusual 
length. The early occurrence of double and multiple leaf-traces 
was found to be very general in the plants examined. 
