OSMUNDACEAE 537 
central pith: as it does so its endodermis opens, and becomes continuous 
with that which completely surrounds the stelar system (Fig. 298 4, B, C). 
The latter, as seen in transverse section, is composed of several layers 
of parenchyma at the periphery: then follows a band of phloem which 
is continuous, but may be uneven in width, extending inwards at the 
medullary rays. Within this are the xylem-strands, which vary greatly in 
number. O. claytoniana may have as many as 40, O. regalis about 15 
(in Fig. 298-4 there are 14). Zodea barbara 8 or less (in Fig. 2988 there 
are 8, in c there are only 3), while in 7. superba the xylem may form an 
unbroken cylinder. The position of the protoxylem also varies: in Osmunda 
it is nearly on the inner edge of the metaxylem, but in Zodea the xylem 
is mesarch, or in Z: hymenophylloides the strands are almost exarch. 
Fic. 298. 
A=diagram sbowing the arrangement of the vascular tissue in the axis of Osmunda 
vegalis (after Zenetti). 3B and C=transverse sections of the stele of Todea barbara, with 
leaf-trace (after Seward and Ford), showing the greater continuity of the xylem than in 
Osmunda. s=phloem. s/=sclerotic tissue. 
Centrally lies the pith: in some cases an internal endodermis is present 
(O. cinnamomea, T: hymenophylloides), while in the former species some 
internal phloem has been found locally in several specimens examined 
by Jeffrey! and by Faull.? 
If the course of the several strands be followed they are found to fuse 
downwards according to a regular scheme, so that they form a cylindrical 
network, of which the meshes are very long and narrow: the number and 
proportions of these vary in different cases, but in all the inter-communication 
of the whole system is exceedingly close and effective. The scheme is 
represented for Osmunda in Fig. 2994, as flattened into a single plane, 
and for Zodea, where the number of the strands is less, in Fig. 2998. 
A comparison of these diagrams with the figures of transverse section 
will explain the main features of the system of the axis. 
There are two possible views as to the nature of this system of the 
axis, as seen in the living Osmundaceae : either that it is a result, of reduction 
1 Phil. Trans,, vol. cxcv., p. 219, etc. 
26 Anatomy of the Osmundaceae,” Bot, Gaz., 1901, p. 381. 
