LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
573 
which Sadebeck followed the development; and as I have observed also in Aspidium 
Filix-Mas, Polypodium vulgare, and Onoclea ( Struthiopteris) germanica, &c. The 
formation of the pinnae in these cases is, at least at first, by monopodial branching, 
though it has been clearly shown that dichotomy may occur in the higher ramifica¬ 
tions of the leaves of some Ferns, 
Taking first Aspidium Filix-Mas, the marginal series of cells could not be distinctly 
traced as continuous to the extreme base of the phyllopodium in the young state, as 
is the case in Ceratopteris, and presumably also in Trichomanes; but such marginal 
series are clearly marked at the periphery of the pinnae, and up to the extreme apex 
of the leaf. There is, however, a longitudinal weal on each side of the base of the 
phyllopodium, which is continuous upwards, with the usual winged development on 
the phyllopodium and the pinnae, and it may easily be recognised in the mature leaf. 
This is doubtless the representative of, or a suppressed form of the wing-like develop¬ 
ment, which is, as iu the cases before described, continuous to the base. In Onoclea 
germanica * the laterally widened basal part of the phyllopodium shows a similar 
external conformation to that in Aspidium, but the two marginal weals project more, 
and, as in Aspidium, may be easily recognised by their white colour. There is, 
however, no distinct development of wings in the usual sense of the term. Thus in 
the Ferns named, and they are merely taken as examples, the marginal developments 
may be traced to the base of the phyllopodium, and it may be concluded that this is 
a usual, if not a constant character for the Ferns. If this be so, the phyllopodium of 
the Ferns is typically a winged structure throughout its length, but in certain parts, 
and especially towards the base, the wings may be reduced, and only be recognised in 
the mature state as giving an angular form to the transverse section, or as light 
coloured, and very slightly projecting longitudinal ridges. 
The Hydropteridece are probably close allies of the other Leptosporangiate Ferns, 
but with their vegetative organs reduced in accordance with their aqueous habit. In 
this group there is a general reduction of development of the leaves, which, however, 
is apparent in different ways. Thus in Azolla there is a reduction of the phyllopodium 
to a minimum (if indeed the term may be applied at all), while the leaf has hardly any 
characters in common with the Fern-type. In Salvinia the early development of the 
leaves shows more points in common with the Fern-type, there being a two-sided apical 
cell, and, at least in the aerial leaves, a series of cells at each margin of the flattened 
leaf, similar in position and origin to that in the Ferns (compare Pringsh. Jahrb., 
Tom. 3, Taf. 25, fig. 7). In Marsilia the leaf is not of so reduced a type, and shows 
a clearly marked relation to the Fern-type. As shown by Hanstein,-]- there is at first 
* This plant lias been noted by Goebel (Bot. Ztg., 1880, p. 787) as an example of the occurrence of 
scale-leaves; some of the leaves lose their apical portion, which dries up, and is thrown off, while the 
basal part remains persistent. In the plant of Onoclea, which I had under observation, about half of 
the leaves had thrown off their apices in this way: the form of the basal portion which persists does 
not differ in any marked degree from the bases of the normally developed foliage leaves. 
f Pringsh. Jahrb., Tom. 4, p. 245, &c. 
