Affinities of Helminthostachys zeylanica. 435 
separated from them by one or more layers of parenchyma. 
It is apparently connected with the foliar gaps, for in a few 
instances the tissue in question was traced as a direct continua- 
tion of the outer endodermis, being connected with it over 
the margin of the gap. This direct connexion can, however, 
by no means always be made out, even when the gap is a wide 
one, the outer ring ending at the margins of the gap or merely 
bending out over the leaf-trace, but not dipping into the 
interior of the stele. In any case, however, the distribution 
of the inner ring is irregular in most places ; often the 
characteristic markings can only be observed on groups of 
cells which are separated from the next part of the band by 
normal parenchyma from which the cuticularisation is absent. 
It is however very constantly to be met with inside the stele 
at a spot where a vascular strand to a root is emitted. In 
fact the inner endodermis may be roughly compared to a sort 
of irregular net-work on the inner side of the xylem. Its 
existence is of special interest, as Poirault 1 mentions and 
figures an inner endodermis for the young stem of Botrychium , 
but states that it becomes indistinguishable in the larger stems 
of older plants. In Helminthostachys , however, precisely the 
reverse would appear to obtain ; for whilst it is extremely 
obvious in all the older rhizomes which we examined it is 
certainly not so in the young stems ; although a slight 
indication of radial thickening was seen here and there it did 
not answer to the tests of either stains or treatment with 
sulphuric acid. On the whole it seems clear that its occur- 
rence is secondary ; and as already stated, is connected with 
the opening of the strand where the leaf-traces originate, just 
as was ascertained by Leclerc du Sablon 2 for Osmunda and 
Pteris , save that in these plants the case is still further com- 
plicated by the presence of internal phloem, and that \x\ Helmin- 
thostachys the endodermis does not, as apparently in them, 
line the inner part of the stele as a continuous sheet of tissue. 
1 Poirault, loc. cit. 
2 Leclerc du Sablon, Recherches anat. sur la formation de la tige des fougeres. 
Ann. Sci. Nat. (Bot.), ser. VII, t. XI. 
