532 Gzvynne- Vaughan.—Some Remarks on the 
From the above considerations, again, it is evident that the structure 
of the sporeling will not conclusively decide whether the pockets or the 
pith were the first to appear in the phylogeny of the Osmundaceae. Some 
facts bearing upon this question may be obtained from the fossil representa¬ 
tives of the order. In the first place Thamnopteris and Zalesskya ) which 
have a solid xylem with a central mass of short thin-walled tracheae, show 
no trace of pocketing whatever. It must not be taken, however, that this 
fact excludes the possibility of the appearance of pockets before the forma¬ 
tion of a pith. In both these genera the leaf-trace at its actual point of 
departure is rounded or elliptic in section, and it is easily seen that there 
would be no encouragement to form a pocket in the axil of a leaf-trace of 
such a form. The mesarch traces in the sporeling of Osmunda regalis are 
similar in section, and in this case also a pocket is never present. The 
formation of axillary pockets is clearly related to the departure of leaf - 
traces which are adaxially concave at their very point of origin. If, indeed, 
such a thing ever existed as an Osmundaceous stem with a solid xylem 
and leaf-traces gutter-shaped at the very point of their departure, it is quite 
to be expected that there will also be xylem-sheath pockets in the periphery 
of its xylem. In Osmundites Dunlopi , the nature of the pith of which is 
unknown, the pockets are very small, and rarely, if ever, break the continuity 
of the xylem-ring. On the other hand, in Osmundites Kolbei , which has 
a mixed pith, the pockets are so deep that they break up the xylem-ring 
into separate strands. At the same time they are not so well developed as 
in the modern Osmundaceae, for the interruption of the xylem-ring is 
seldom completed at the actual level of the departure of the trace, but only 
at a point some distance above. 1 It would appear, therefore, that the 
relative development of pithing and of pocketing was not uniform, but 
probably varied in different lines of evolution. 
Two conclusions as to the nature of these nodal pockets are possible. 
The one that I would bring forward is that the xylem-sheath pockets are 
a relatively primitive feature in the order, and that they were primitively 
associated with protostelic leaf-traces, which departed without leaving 
a gap in the xylem-ring. Such protostelic departures with pockets are 
still to be found in the sporelings of Osmunda regalis and O. cinnamomea , 
and in the latter they sometimes even occur in adult plants. 2 I have also 
described similar cases in Todea . 3 The accuracy of this statement has since 
been called into question by E. W. Sinnott. 4 My observations were made, 
it is true, from hand-cut sections and not from microtome series, but in 
the light of Faull’s results I still venture to think they are correct. 
1 Kidston and Gwynne-Vaughan, 1 . c., Pt. IV, p. 459, Fig. 3. 
2 Fanil, 1. c., pp. 517 and 523. 
8 Kidston and Gwynne-Vaughan, Pt. I, p. 775. 
4 Sinnott, E. W. : Foliar gaps in the Osmundaceae. Annals of Botany, vol. xxiv, 1910, p. 109. 
