2 54 
Davie.— The Structure and 
and strongly recalls the receptacle of the Cyatheaceae, are inserted some 
four hundred sporangia. Young and old sporangia are inserted pro- 
miscuously round the receptacle, a predominance of younger ones occurring 
towards the lower edges (Figs. 14 and 15). Young ones also occur at the 
apex of the receptacle among the stalks of quite mature sporangia (Fig. 14). 
The sorus is thus one distinctly of the mixed type, upon a receptacle 
characteristic of the Gradatae. The presence of younger sporangia towards 
the lower edges of the receptacle confirms the suggestion of the derivation 
of this sorus from one of a Gradate type. 
There is no regularity of orientation among the sporangia in the sorus. 
Their annuli are arranged pointing in all directions when looked upon 
from above. 
The sporangium itself is long-stalked, the stalk often taking a slightly 
curved form, the convex side of the curve being on the same side as the 
annulus (Fig. 16). Two or even three series of elongated cells are found 
contributing to the length of this stalk. In section the stalk consists of 
three cells symmetrically arranged about the centre, one rather larger than 
the other two (Fig. 17) as in N ephr odium. The capsule is rather elongated, 
much like the capsule of a typical Polypodiaceous Fern. The annulus 
consists of twelve to fourteen cells, indurated on the four sides, though, as 
usual, least strongly on the outer walls (Fig. 16). It passes right over the 
top of the capsule, and is continued always right back to the stalk as an 
unbroken and symmetrical series of typically indurated cells (Fig. 16). 
Frequently indurated walls are found in the cells past the stalk, though 
more commonly the induration stops in the one just at its centre. The 
series of cells of the annulus is, however, always continued past the stalk. 
As this stalk consists of three cells, they are arranged in a group of two on 
one side of the capsule, with the single one on the other side. The annulus 
is continued to one side of the single one, passing right across the tops of 
the cells in the other two (Fig. 18). It is thus slightly oblique in its 
insertion (Fig. 19). 
The stomium consists of a series of wide cells, often seven in number, 
which continue and complete the hoop of the annulus round the sporangial 
head. Two of these cells are always strongly indurated, and are wider 
than the rest (Fig. 20). It is between these that the first break occurs, 
which allows the mechanism of the annulus to work and to secure the 
dispersal of the spores. The dehiscence of the sporangium takes place by 
a series of irregular cracks stretching across the sides of the capsule from 
the stomium. 
The spores within each sporangium appear to number sixty-four. This 
number is characteristic rather of the Gradatae than of the Mixtae, though 
it is a feature to be anticipated in view of the elongated receptacle and 
the slight obliquity of the annulus. These three features of sorus and 
