8o GYMNOGRAMMOID FERNS [CH. 



The origin of the pinna-trace is extra-marginal, as it is also in Notholaena. 

 In all these points Adiantiim fits naturally in with other Gymnogrammoids. 



In the epidermis of the blade of Adiantmn "spicular cells" have been 

 found, the significance of which will appear in relation to the Vittarieae 

 (see Chapter XLVll). 



The sori consist of sporangia inserted 

 upon the distal region of the separate veins 

 of the reflexed lobe. This is the usual type, 

 and it has been held as the character 

 of the section En- Adiantiim Kuhn. But 

 sometimes the sporangia may spread also 

 on to the surface of the blade between the 

 veins, giving thus as in Gyvinograimne 2ind Fig. 634. Adiantmn macrophyilwn Sw., 



7- • i- 11 A 4.- 1 • 1 J. i. fertile leaf-lobe, with sporangfia inserted on 



Jamesoma an essentially Acrostichoid state. ^^^ p.^enchyma between the%ein.s. (After 



This has been taken as the diagnostic charac- Frau Eva Schumann.) 

 ter oi Adiantelbun Kuhn, and it is seen in A. macrophylluin Sw. (Fig. 634). 

 Dr Horvat has described for old prothalli of AdianUuii a structural 

 peculiarity which bears some degree of significance. Bauke had many years 

 ago noted a collenchymatous thickening of the walls in the prothalli of 

 Anemia {Yx\ng^\)..Jahrb. 1878, p. 628, Taf XLI, Fig. i): and a like structure 

 was found by Heim in Lygodinm {Flora, 1896, p. 368). Thus it appears in 

 representatives of both series of the Schizaeaceae. Dr Horvat (1923) finds 

 that similar collenchymatous thickenings appear in Adia?itnm, and he has 

 since described a like structure in CJieilanthes (1925) (compare Fig. 635, i, 2). 

 The comparative significance of this will be considered again later. 



2 



Fig. 635. i=a cell from the flap oi an old prothallus of Anc7nia phyUitidis: 

 the walls show a peculiar bead-like thickening. 2 = cells from the prothallus 

 of AdianUim cuneatuin L. and F. (After Horvat.) 



Adiantiim appears as a clearly defined and somewhat isolated genus. It is 

 not difficult to see how it may have originated from a source related to other 

 Gymnogrammoids. The effective protection of the sori while young, by the 

 close folding of the distal end of the blade, would in itself help to explain 

 the success of the Maidenhair Ferns, as measured by the large number 

 of their species, and by their wide geographical spread. 



