254 GENERA INCERTAE SEDIS [gh. 



MONACHOSORUM Kunze 



Another genus long held as of doubtful affinity is seen in Monachosomm 

 Kunze, which has been discussed in Chapter XXXVI, p. 13: here, however, 

 in addition to other features, the existence of hairs and no scales appears 

 decisive in assigning its place with the marginal series, as a derivative of 

 the Dennstaedtiinae, probably along a line parallel to that of Hypolepis. 



These three examples illustrate the critical questions that arise in placing 

 isolated genera in relation to the greater series of Ferns. Those who attach 

 less importance to the comparative history on which the distinction of the 

 Marginales and Superficiales has been based, may see in them an argument 

 against its validity. On the other hand, those who accept it will see in such 

 problematical genera those very difficulties that were sure to arise as a 

 consequence of progressive evolution, in Ferns of distinct affinity, under like 

 conditions. It may be doubted, however, whether such relatively late 

 developments in the phyletic history, as these genera present, can legitimately 

 provide a basis for criticism of those more general groupings; for these have 

 been founded on comparison of types of known antiquity, as shown by the 

 early fossil records (see Chapter XL, pp. 113-118). 



Prosaptia Presl 



Another striking example of the difficulties that beset a natural classi- 

 fication of Ferns is seen in Prosaptia, a genus founded by Presl in 1836 to 

 receive certain small species already described under Davallia by Swartz 

 {Tentamen, p. 165, PI. vi. Figs. 19, 25). The story how this genus, rightly 

 distinguished by Presl as it now appears, was under the authority of Sir W. 

 Hooker consigned for nearly a century to Davallia, has lately been told by 

 Von Goebel in an essay which may be held as a model for the treatment 

 of such critical questions {Buit. Ann. Vol. XXX VI, 1926'; Morph. 71. biol. 

 Studies, pp. 148-158, Figs. 79-87). He tells how during that century 

 opinion was divided between a Polypodioid and a Davallioid affinity, 

 gradually hardening in the direction of the former. Prosaptia was compared 

 more particularly in habit and in sorus with Polypodium obliqtiatuni Blume. 

 This Fern was included by Fee under his genus Crjptosorns, characterised 

 by the young sorus being sunk in the parenchyma, and subsequently 

 emerging on the surface by a narrow slit. Prosaptia has a similarly sunken 

 sorus, but with the difference that here it lies close to the margin, and is 

 surrounded by a funnel of protective tissue, in the formation of which the 

 margin of the blade takes a part (Fig. 750). The general appearance of the 

 sorus may well excuse a reference to Davallia, § ScypJuilaria Fee: but as 

 Von Goebel shows conclusively, a wider comparison proves this to be 

 fallacious. 



The habit of Prosaptia closely resembles that of Polypodium obliquatum 



