598 FILICALES 
already noted! that the receptacle is derived from the leaf-margin, while 
the cup-like indusium originates as two flap-like outgrowths of the lower 
and upper surfaces; excepting that the indusium is not two-lipped, and 
that the receptacle is cylindrical instead of flattened, it resembles in its 
main features the sorus of Dzcksonta. The relations of the sporangia within 
the sorus have been examined in Dennstaedtia apitfolia, Hook., with the 
result that the basipetal succession has been found to be much: more 
marked than in Diécksonia. The receptacle is cylindrical and elongated, 
and traversed by tracheides for a considerable distance (Fig. 332 2s, A); 
upon it the sporangia arise, as a rule, in strictly basipetal order. The 
sporangia themselves undergo the usual segmentation; when mature they 
Fic. 332 dzs. 
A=Denustaedtia apiifolia, Hook. Sorus showing basipetal succession throughout. 
C=dehiscent sporangium of the same showing very slightly oblique annulus. B= 
Dennstaedtia rubiginosa, geal Sorus in vertical section showing that it has been at 
first basipetal, but with a mixed character supervening. =dehiscent sporangium-of the - 
same, seen from the base, showing that the annulus stops short on either side of the 
insertion of the stalk (s¢), Al1X 100. 
have long stalks composed of three rows of cells; the head is not 
bilaterally symmetrical, but one side is more strongly convex than the other; 
and it will be seen from the figure that the more convex side is the 
peripheral one. The annulus is not exactly vertical, but running round the 
margin of the sporangium to the attachment of the stalk, it is there slightly 
diverted to one side (Fig. 332 ds, c); usually the sequence of cells of the 
annulus is not wholly interrupted by the insertion of the stalk, but its cells 
are more or less in contact with one another, and the annulus is in such 
cases actually continuous at the base, as it is in those sporangia where it is 
more conspicuously oblique. In fact, the sporangium of D. afzifolia shows, 
though in a less obvious degree than in Dicksonia, the oblique annulus. 
The nearer side of the sporangium shown in Fig. 332 dis, c is the less 
convex one, the more convex side is the peripheral face as regards the 
+ Loc. cit., p. 19. 
