446 Scott and Hill.-—Structure of Isoetes Hystrix. 
structure, and their branching monopodial 1 . If the peculiar 
characters of the root in certain species of Ophioglossum have 
any taxonomic significance (a doubtful point, which we can¬ 
not discuss here), they may indicate a certain approach to 
the Lycopods generally, but are no evidence of any special 
relation to Isoetes. The mode of origin of the roots of 
Isoetes has been compared to that in Marattiaceae, but there 
is no real agreement, for the Isoetes roots do not arise near the 
apex, or from the apical meristem, but are always limited to the 
lower part of the stem, and spring from a secondary tissue 2 . 
On the other hand, as already pointed out, they agree in these 
respects with the roots of such species of Selaginella as *S. 
spinulosa. 
Passing on to the leaves, and first considering their anatomy, 
we find that the single bundle, traversing the narrow leaf with¬ 
out branching, is in itself a Lycopodinean character, though 
a similar simple arrangement no doubt occurs in a few 
extremely reduced Filicales. The collateral structure of the 
bundle is unlike that in living Lycopods, so far as at present 
investigated, but agrees with the structure of the foliar 
bundles in the fossil Lepidodendreae. The agreement with 
the latter is far closer than with the large and branched 
collateral bundles in the leaf of Ophioglossum. In other 
respects the anatomy of the leaf in Isoetes affords no taxonomic 
indications. The development of the leaf almost entirely 
by intercalary growth, is, as Wilson Smith has pointed out 
(1900, p. 333), a marked Lycopodinean character, and forms 
a striking contrast to the apical foliar development of Ferns. 
The general morphology of the leaf, i.e. of the sporophyll, 
is however of greater importance than any other character. 
The single large sporangium, seated on the upper side of the 
sporophyll, near its base, in position, development, and struc¬ 
ture is typically Lycopodinean, and has no analogy with 
1 See Boodle, 1899, on roots of Ophioglossum , and especially on monopodial 
branching in those of 0 . pendulum. 
2 The adventitious roots which grow down through the cortex in certain species 
of Lycopodium (e. g. L. squarrosum ) appear to afford a better analogy with those 
of Marattiaceae. 
