534 
Gwynne- Vaughan.—Some Remarks on the 
In well with the theory of the intrastelar origin of the pith in their respective 
orders, but would be meaningless if the pith be extra-stelar. 
It is recognized that, if the Osmundaceous pith is intrastelar, the 
presence in the pith of an internal phloem in Osmundites skidegcttensis and 
Osmunda cinnamomea and of an internal endodermis in Todea hymeno- 
phylloides has still to be accounted for, although this question may be 
taken as apart from, and as having no direct bearing upon, the intrastelar 
origin of the pith itself. As a matter of fact, several possibilities are open. 
In the first place Dr. Kidston and I have suggested that the phloem and 
endodermis may have been decurrent through the branch-gaps info the 
pith. It must be understood that the word ‘ decurrent ’ is here used in 
a special sense, and of course does not imply any actual motion. It is 
meant to imply that the stimulus to produce internal phloem and endo¬ 
dermis originated at the margins of a branch-gap, and phylogenetically was 
gradually transmitted to lower levels in the stem. To this idea Faull objects 
that he has found internal phloem in plants of Osmunda cinnamomea that 
have not yet branched. I do not see that this affects the question. If the 
internal phloem and endodermis in their present state of development are 
decurrent for some distance below the point of branching, the apical merl- 
stem must form them in this region some time before it branches. 
A second alternative, and a very probable one, is that the internal 
phloem and endodermis may have arisen entirely de novo in the intrastelar 
pith, and that subsequently connexions were established with the corre¬ 
sponding external tissues. 
A third possibility is that some time after the formation of an intra¬ 
stelar pith the outer phloem and endodermis were invaginated into the 
same through the leaf-gaps. Faull 1 figures a case in Osmunda cmnamomea 
in which the two endoderms are in continuity through a leaf-gap. To me, 
however, his figure suggests that the internal endodermis has reached out¬ 
wards to meet the external rather than vice versa. 
As matters stand, however, it is in no way incumbent on a supporter 
of the intrastelar theory to pin his faith to any one of these suggestions. 
The fossil evidence in the Osmundaceae I regard as distinctly in favour 
of the intrastelar nature of the pith, since it has brought to light Osmundites 
Dunlopi , the mixed pith in Os?nundites Kolbei , and also the short tracheae 
in Jhamnopteris and Zalessky a. Dr. Kidston and I believe that in Osmun¬ 
dites Dunlopi the pith is surrounded by an uninterrupted ring of xylem, but 
even if this be not so it would still represent an important transitional stage 
between a continuous ring and well-defined leaf-gaps which in any case 
must have existed. Both Faull and Sinnott have laid more stress upon the 
imperfection of this fossil than it really deserves, for in our description of it 
we have been far from lenient. It is true that the interpretation of fossil 
1 1 . c., Fig. 11 
