XLII 



ATHYRIUM 



143 



morphic sorus, which was initiated from the more ancient radial type along 

 such a series as Gleichenia, Lophosoria, Alsophila, Heinitelia, and Peraneina. 

 The zygomorphy was slight in Peraneina, but already it was marked by 

 those lateral pouches of the fertile receptacle, which became more elongated 

 in the Dryopteroid Ferns (see Chapter XLI, p. 124). One or both of these 

 find their extreme form in the actual sori respectively of Aspleninvi and of 

 Diplaziuni, while the central part of the receptacle, which was the original 

 fertile region, has dropped out of functional development. Meanwhile it is 

 only the lateral lobes (both or only one) of the indusmni supernvi which 

 survive. Without the intermediate steps it would be difficult to trace in the 

 Asplenioid indusium the correlative of a part of the Cyatheaceous ///^///j7V/w 

 inferuni. 



Fig. 672. 1-6 = drawings from sori all borne on the same leaf of Diplazium 

 lanceum Thunb. , showing stages that illustrate steps between the Dryopteroid 

 sorus (1-3) and those of Diplazium (4, 5), and Eii-Aspleniitm (6). (From a 

 specimen in Kew Herbarium under name Aspleniiiin lanceiDU, Napalia. Dr 

 Wallich, 1829.) 



xA^THYRIUM Roth 

 Additional evidence of the correctness of these comparisons may be found 

 in the ^^mxs Athyriiini, which there is reason to believe is more nearly related 

 to Dryopteris than is Asplcnhcm itself. It comprises Ferns with creeping, 

 but more frequently with ascending or upright stock, on which the leaves 

 are borne spirally. Sometimes these Ferns are almost dendroid. Thin-walled 

 scales are present, not the latticed scales of Asplenium. The adult stem 

 contains a rather wide-meshed dictyostele. The petiole is traversed at its base 

 by two broad straps of the leaf-trace, as in Dryopteris TJielypteris (L.) A. Gray, 

 and PolysticJmm loncJdtis (L.) Roth: these unite below the blade to form a 

 gutter-shaped meristele. The leaves are at least once, and usually twice or 

 thrice pinnate, and the venation is open. The sori and indusium are oblong, 



