Bower.—Studies in the Phytogeny of the Filicates. 427 
sclerotic covering to the softer tissues within. Passing upwards the enlarged 
leaf-base tapers gradually without any definite limit into the petiole, which 
is more or less clearly four-angled, while dwarf wings project slightly from 
the lateral faces. In the upper region of the leaf the pinnae are inserted 
upon these wings ; in P. pycnophylla the pinnae are some little distance 
apart from one another, and are very shortly stalked, but in P. semicordata , 
especially towards the tip of the leaf, they run together at their bases, so 
that the rachis is quite continuously winged ; these features are repeated 
in the fertile leaves, though in less pronounced degree (PI. XXXII, Figs. 1 
and 2). The venation is of the sub-Taeniopterid type (Mettenius, 1 . c., p. 1), 
and the forking of the veins is inconstant; a considerable number of them 
run to the margin unbranched, there traversing the minute serrations which 
are specially prominent in P. semicordata. 
In the young circinate condition the leaves are completely covered 
with a dense felt of curly hairs, which are septate, unbranched, and 
terminated by a single large cell with mucilaginous contents; in essentials 
they are similar to those of the leaves of the Osmundaceae. Peltate scales 
are entirely absent, as noted by Mettenius ( 1 . c., p. 1). In this condition 
the young leaf is completely protected from risks of evaporation from its 
surface. The felted covering is more strongly developed in P. pycnophylla 
than in P. semicordata or glauca. 
Probably in intimate relation to this is the development of those 
‘ aerophorae ’ described by Mettenius, or pneumatophores as they would 
now be called. Their presence on the leaf-base has already been noted, 
and drawings of them are given in most illustrated treatises; they are here 
represented as seen on the bases of young leaves of P. glauca in P'igs. 3 and 4. 
In the upper region of the leaf they were also recorded by Mettenius as 
occurring in P. pycnophylla , one at the base of each pinnule; here they 
are clearly to be seen in the mature leaf (Fig. 1) ; but it is in the young 
condition, while the leaf is still circinate, that they are most prominent 
(Figs. 5 and 6). In P. semicordata , though the pneumatophores are present 
on the leaf-base, they are not recognizable on the distal region of the leaf. 
This may be put in relation with the fact already noted that the hairy 
investment is less developed in this species than in P.pycnophylla} 
1 Pneumatophores are well known as prominent objects on the leaf-base in the genera Alsophila , 
Hemitelia , and Cyathea , where they are often of large size; in the mature state of the leaf they 
appear as roundish or oval pores traversing the hard sclerotic coat, and are filled with friable and 
dry tissue (see Mettenius, 1 . c., pp. 3-5, where are also references to other writers). In the upper 
leaf of these herns there are along the marginal wings, and especially close to the bases of the pinnae 
and pinnules, pale and slightly turgid spots, which show by the presence of stomata and by the 
spongy subjacent tissue that they are of importance for ventilation. They do not, however, project 
beyond the surface to any considerable degree. But occasionally at spots corresponding to these 
the tissues grow out into processes of considerable size, and the 1 aerophorae ’ or pneumatophores 
in the upper leaf of P. pycnophylla are cases in point. Similar processes are seen also in Dryopteris 
( Polypodnim) decussata , (L.) Urban, and in Dryopteris {Polypo dinin') Thomsonii , (Jenm.) C. Chr. 
