460 OPHIOGLOSSALES 
that all the three genera show either a solid xylem-core or a slightly 
medullated stele in the young axis. 
Proceeding to the upper part of the shoot the medulla increases, while 
the vascular tissue forms a more or less interrupted cylinder surrounding 
it: the interruptions are the leaf-meshes, for above the exit of each leaf- 
trace there is a gap in the cylinder. In Ophzoglossum the meshes are large, 
and as the leaves are arranged in a compact spiral, the whole system assumes 
a form clearly shown in Rostowzew’s drawings (Fig. 236, Nos. 4, 5). In 
Botrychium a similar arrangement is found; but as the proportion of the 
leaf-meshes to the whole surface of the cylinder is less, it approximates 
more nearly to a continuous tube. This is still more clearly seen in 
Lelminthostachys, where the shoot is 
dorsiventral ; for there the foliar gaps 
are disposed obliquely upon the 
upper side only of the cylinder, while 
the lower side of it is uninterrupted 
(Fig. 257). It would thus appear 
that the vascular system of the axis 
is essentially similar in them all, and 
is referable in origin to the amplifi- 
cation of a primitive stele, with a 
distending pith, and perforation of 
the vascular cylinder by foliar gaps. 
As regards the tissues themselves, 
the most important of them for 
Rigioee: comparison are the xylem and the 
Hebuinilosathys-aianiza, Hooks. ‘The upper endodermis. The latter shows 
figure represents the vascular skeleton, dissected out. curious irregularity of occurrence in 
L=leaf-trace; 2 =root-strand; Fg=foliar gap. The 
lower figure shows the rhizome-stele giving off a leaf- this family. In Botrychium there 
trace, £.7., which breaks up above into separate 
petiolar bundles. &=root-trace. (After Farmer igs g well-marked outer endodermis 
and Freeman.) 
throughout the length of the stock: 
there is also an inner endodermis in the pith, but it is found only at 
the base of the stock (Poirault). In most species of Ophzoglossum 
there is no endodermis in the stock at all; but in O. Bergianum, 
capense, and elipticum, all small species, an outer and inner endodermis 
are both present, though at the base of the stalk only: passing upwards 
they fade gradually away, the inner disappearing first.1 In Helmintho- 
stachys, curiously enough, the converse is seen: here there is throughout 
the stock a well-marked outer endodermis, as in Botrychium, but the inner 
appears only in the older stems, the young plants being quite destitute of 
it.2. It is difficult to draw any definite conclusions from such discordant 
facts: it must suffice for the moment to remark that, on the one hand, 
there is want of constancy of the endodermis also in the Psilotaceae, and 
on the other, that in the Marattiaceae the endodermis is present in 
1Poirault, Zc., p. 169. 2Farmer and Hill, Azz. of Bot. xvi., p. 401. 
