rOLYPODIACE^S. 331 



with the edge more or less elevated ; then the sporangia come into sight. 

 When fully grown, it becomes a sorus different in appearance from that of 

 Cryptosanis, but very similar to that of Davallia. Yet, gradually transitional 

 forms between this Davallia-\\ke> sorus and the normal Cryptosorus-likG sorus 

 are to be found in the development of the fructification in Prosaptia, and also 

 are to be seen in the full grown sorus of Polypodium urceolare, as I have stated 

 before. Consequently, Prosaptia is in its vegetative as well as its propagative 

 organs so closely related to Polypodium phylogcnetically that it is quite proper 

 to unite them into one genus. 



Now let us consider whether the resemblance of Prosaptia and Davallia 

 which seems apparently very close is really an indication of phylogenetic kin- 

 ship or a mere accidental feature. To decide this question fundamentally 

 I made the same study on Davallia, as I had done before on Cryptosorus and 

 Prosaptia. Davallia is a fern not of indefinite, but of definite growth, and 

 all the sori in one frond mature simultaneously. I took a young shoot of D. 

 Itullata nearly 5 cm. long, just coming out from the rhizome, partly coiling 

 and partly unfolded, yet bearing beautiful sori of a veiy young stage. I 

 examined the frond under a binocular microscope with object-glasses a L , and 

 found the sori in a stage just before sporangium-formation. Indusium-fornia- 

 tion was just beginning a little below the apex of the lobes. The indusium 

 (Fig. 137, k) was coming out like a broad quadrangular scale, attached at its 

 base to the surface of the frond, but leaving its margin quite free from the 

 latter. There was no depression whatever. The type of this kind of indusium 

 is represented in a full grown sorus of Humata. It is totally different from 

 the type seen in Prosaptia. It is, therefore, highly probable that Davallia is 

 derived directly from Humata ; and Prosaptia, from Polypodium. Consequently 

 it is clear that the resemblance of Davallia and Prosaptia is a mere accidental 

 feature. The two can never be united into one, nor should the one be treated 

 as a subgenus of the other. One might as well take a pseudomorph for a true 

 crystal, as to take Prosaptia for a Davallia. 



After considering all the above mentioned cases, I have been led to con- 

 clude that Prosaptia in the first place should be taken into Polypodium and 

 for convenience sake retained as a subgenus of the latter, as is the case with 



