26 Bower.—Studies in the Phytogeny of the Filie ales* VII. 
naturally sections of the young state give more direct evidence (Fig. 
22 bis, b), the oldest sporangium being seated on the apex of the convex 
receptacle. Such sections also show the inconstancy of the inner indusium ; 
but it is often difficult to distinguish between the youngest sporangia and 
the primordium (or vestigium) of the inner indusium. Thus, in Fig. 
22 bis , B, it is uncertain whether the lowest abaxial growth is of indusial 
or of sporangial character. In Fig. 22 bis , C, it is almost certainly an 
indusium. A 
Fig. 22 bis. A-c. Vertical sections through the sorus of Paesia scaberula. ( x 150.) 
Thus the general condition of the sorus compares with that of Pteri - 
diurn in being basipetal and typically bi-indusiate ; also in the inconstancy 
of the inner indusium. Material did not suffice for tracing the relation 
of the receptacle to the marginal segmentation of the leaf. But comparison 
would indicate with a high degree of certainty that the receptacle is marginal 
in origin as in Pteridium. All the indications point to a very close relation 
of Paesia to that genus. 
