Osmundacece. 
261 
stems of very young plants (Fig. 89), and no internal phloem was 
found anywhere. 
In Osmundites skidegatensis Penhallow (Fig. 90), the type of 
structure is like that of Osmunda cinnaniomea, except that the internal 
phloem of the stele is constant, and is continuous with the external 
phloem through each leaf-gap, while the whole vascular cylinder is 
interrupted at the leaf-gaps, the pith coming into connexion with 
the cortex, so that we have a true dictyostele produced, differing 
from the ordinary dictyostelic type of the higher Leptosporangiate 
Ferns by the extreme narrowness of the gaps, by the characteristic 
shape and course of the xylem-strands and by the other anatomical 
features peculiar to the Osmundaceze. 
it. 
A 
B 
C 
Fig. 89. Todea liymenophylloides. Successive stages in the evolution of 
the stele of the young plant. A.—Stage with protostelic solid xylem. B.— 
Stele with pith showing “protostelic” departure of leaf-trace. C.— Xylem 
cylinder showing three distinct strands. From Seward and Ford. 
It is thus obvious that we have, in the Osmundaceze, a continuous 
series of types of stem-structure, beginning with such a form as 
Osmundites Dunlopi (represented also in the first-formed stems of 
living types—Fig. 89, B) and ending with the complex structure of O. 
skidegatensis. The considerable resemblance between the simplest 
form of Osmundaceous stele, with continuous xylem, and such a 
form as Zygopteris corrugata is striking enough, while the apparent 
primitiveness of the Osmundaceous sporangium and its resemblance 
to the Botryopteridean type renders the hypothesis of a real phylo¬ 
genetic connexion between the two types of stele decidely probable. 
This probability is, however, very greatly increased by the quite 
recent, and as yet unpublished, discovery by Kidston and Gwynne- 
Vaughan of undoubted Osmundaceous stems connecting the type of 
O. Dunlopi with such a form as Renault’s Grammatopteris Rigolottii 
(see p. 55). The evidence for regarding the Osmundaceous series 
as an ascending one has thus become all but overwhelming. 
On the other hand Fattll and Jeffrey have contended that the 
state of things seen in 0 . cinnaniomea, in which internal phloem 
