io6 Davie. — -The Development of the Sorns and Sporangium 
base and the oblique first wall correspond to similar features in the 
sporangia of Thyrsopteris and Alsophila (loc. cit., pp. 590, 603). The early 
segmentations in the sporangia in Text-fig. 2, <?, g, and h, are of the 
Cyatheaceous type. Those found in c and d are apparently also to be found 
in some species of Nephr odium (Ktindig, ’88). The early divisions shown in 
b and f resemble those in the Polypodiaceous sporangium, to which the 
mature sporangium of Peranema , with its long stalk and almost vertical 
annulus, bears some resemblance. Thus some sporangia figured resemble 
those of the Cyatheaceae, others those of the Polypodiaceae. And as 
a whole the sporangium of Peranema is intermediate between those charac- 
teristic of the Cyatheaceae and those found in the Polypodiaceae, although 
there is in it a preponderance of Cyatheaceous characters. We have then 
to set against a distinctly Nephrodioid vascular system, mixed sorus and 
‘ aspidioid ’ spores (Davie, T 2 , pp. 255, 264), a Cyatheaceous indusium and 
early sporangial segmentation, a Gradate receptacle and early sporangial 
sequence and spore-number (loc. cit., p. 254). We conclude that Peranema 
is a Fern descended from a Cyatheaceous line and somewhat advanced on 
the main Cyatheaceous type towards a ‘Nephrodioid ’ type. 
This is interesting, apart from general phyletic considerations, in the 
light which it throws upon the sorus of Nephr odium. If the whole of one 
side of the cup of the Cyatheaceous sorus were to be suppressed, and the 
other side much developed so as to overarch the receptacle, we should have 
the type of Nephr odium. In Peranema we have in the early sorus a partial 
suppression of the one side of the cup and a great overarching development 
of the remainder of the indusium. If we for the moment neglect the 
presence of the stalk, we have in the early Peranema sorus the intermediate 
stage between the type of the Cyatheaceous sorus and that of Nephr odium. 
The extension of the sorus of Peranema beyond the level of the leaf-surface 
seems to permit of an increase of the receptacular area upon which the 
sporangia may be developed. In well-developed sori the sporangia are 
actually produced all round the stalk (cf. PI. Ill, Fig. 6 ). Even in the ordinary 
sorus there is a tendency to extend the receptacle upwards towards the 
leaf-surface (the figures of the sorus are reversed from their natural position, 
since in nature the sorus grows vertically downwards from the under surface 
of the leaf), while the indusium becomes very much stretched out over this 
extension. The section figured in Fig. 6 was cut transversely to the stalk, 
just above the junction-point of stalk and sorus, and it shows how the large 
‘ flap 5 of the indusium becomes extended on the side of the stalk from which 
it arose and pushed some distance along the stalk as two narrow pouches. 
In the sori of Nephrodium and Polystichum the receptacle is present round 
the stalk and, in Nephrodium , forms two pouches on one side of it — making 
the lobes of the ‘ kidney ’. In Peranema , however, the receptacle is always 
above the indusium ; in Nephrodium and Polystichum it comes to be below. 
Apparently there arose in the sorus of Peranema a need for space in 
which to develop more sporangia. Instead of the receptacle being length* 
