XXII] COMPARISON 173 



and detail of the sporophylls may appear to vary in high degree, they all 

 are constructed on the same fundamental plan. The solitary occurrence, 

 and uniformly marginal origin of the sporangia, are regarded as primitive 

 features: nevertheless, the sporangia may in various degrees be thrust down 

 to the lower surface as they mature, a position that is already conspicuous 

 in the early fossils, naturally seen only in the adult state. The protective 

 flaps that invest the individual sporangia in modern forms are absent in 

 Palaeozoic and Mesozoic fossils: but those seen in the Schizaeaceae of the 

 present day offer peculiarly suggestive comparisons with the indusia of the 

 Dicksonieae and Hymenophyllaceae, thus linking with the more advanced 

 Marginales. 



The sporangia themselves are uniform in their general features, such as 

 the short thick stalk, and the more or less spherical capsule with longitudinal 

 dehiscence, operated by the distal annulus. This is least specialised in the 

 ancient Senftenbergia, which compares on the one hand with the Palaeozoic 

 Ferns of Osmundaceous affinity (Zeiller), and on the other through Lygodmni 

 with the modern types having a single ring of annular cells. In living forms 

 the segmentation of the young sporangium and its massive stalk link the 

 Family on the one hand with the more primitive types, and on the other 

 with the more advanced Leptosporangiates: a comparison which is further 

 strengthened by the spore-output per sporangium. Lygodiuni, already 

 marked off as relatively primitive by other features, has a typical number of 

 256 spores, corresponding to the simpler Osmundaceae and Gleicheniaceae: 

 but the Schizaeaceae mostly have a typical number of 128, which is lower 

 than that of most Osmundaceae and other Simplices, though it is in excess 

 of the number in most Leptosporangiate Ferns. These soral and sporangial 

 characters point clearly to a position among the Simplices, but indicate the 

 Schizaeaceae as intermediate between them and Leptosporangiate Ferns. 



With such indications drawn from the sporophyte it becomes a question 

 what interpretation is to be put upon the features seen in the gametophyte, 

 and especially upon that filamentous type of it seen in Schisaea. Goebel 

 {I.e. p. 956) by speaking of the prothallus of Schizaea as "blind" to more 

 intense light, and as persisting in the juvenilefilamentous state, appears to hold 

 it as primitive, and assent may be given to this view. These are the simplest 

 prothalli among the Pteridophytes, while the distal position of the antheridia 

 and archegonia on short branches suggests at once Algal comparisons. 



It is thus seen how interesting is the position of the Schizaeaceae in 

 phyletic comparison. Their undoubted antiquity, and their clear affinity on 

 the one hand with the Simplices and on the other with those Gradate 

 Leptosporangiates that have marginal sori, are wholly in accord with that 

 unusual combination of primitive and advanced features which is disclosed 

 by the study of their living representatives. 



