ii6 DRYOPTEROID FERNS [CH. 



and that the soral distinction is sometimes so insignificant that in certain forms the 

 suspicion asserts itself that specimens with and without indusia may be included under 

 both genera. Such observations offer a trenchant commentary upon the supposed constancy 

 of the indusium in these general They open the door to a theory of upgrade origination 

 of an indusium, as a new and independent but fluctuating protective organ among the 

 Cyatheaceae. Let us see how such an idea would accord with a wider circle of facts. 



The fundamental position from which any argument as to the origin and nature of the 

 '■'■indusium inferum'''' of the Superficiales must start is, that these Ferns formed a con- 

 secutive phylum from early Mesozoic times. A modern representative sequence for 

 comparative purposes (not necessarily members of an actual line of descent) has been 

 indicated as consisting of Gleichenia (and in particular Eu-Dicranopteris pectinata)^ 

 Lophosoria and Metaxya, Alsophila, Hentitelia, and Cyathea. The Woodsieae will be 

 considered separately later. The Gleichoiia-iy^e, dating from the Jurassic period, has a 

 simple sorus without hairs or indusium {Phil. Ti-ans. B, Vol. 192, Plate 2. Also Ann. of 

 Hot. XXVI, Plate xxxiv). Lophosoria has also a simple sorus and no indusium, but hairs 

 are present scattered among the sporangia: they are particularly numerous below them, 

 forming a fringe round the base of the receptacle {Ann. oj Bot. xxvi, Plate xxxv. Figs. 28, 

 29, 'i'h- Sometimes they are fused laterally, as in Fig. 25). They have basal intercalary 

 growth, which is common for these soral hairs. Metaxya has a simple but flat and crowded 

 sorus, and no indusium : but hairs are profusely scattered among the sporangia, particularly 

 below those that are marginal {Ann. of Bot. xxvil, Plate xxxii. Figs. 5-9). Alsophila 

 corcovadense {Ra.ddi) C. Chr. { = A. Taenitis Kze.) has its sporangia "mixed with long 

 copious hairs" (Hooker, Gen. Fit. Tab. xxxiv). Hairs are present sparingly in the young 

 sorus of ^. atrovirefis (Vol. II, Fig. 564), but they are present in large numbers and specially 

 at the base of the receptacle in A. excelsa (Hooker, Gen. Fil. Plate ix. Fig. 6). In this con- 

 nection it is to be remembered that Christ also noted the hairiness of the receptacle of 

 Alsophila., and that here and there a scale is found at the base of the sorus, fringed, short, 

 and caducous. Heniitelia bears a more definite and constant scale, similarly placed, and 

 with regular orientation. In H. capense it is shown, fringed and short, by Hooker {Gen. 

 Fil. Plate XLli, A). Hairs are present also scattered among the sporangia (Fig. 566). In 

 H. horrida the scale is larger, and semi-lunar, with an irregular margin (Hooker, Gen. 

 Fil. Plate iv). The last step is the completion of the cup-like indusium, occasionally seen 

 in H. horrida (Mettenius, I.e. PI. xxix, Fig. 5), but typically present in Cyathea (Figs. 

 577, C, and 565). Nevertheless the inconstancy of the indusium in this genus, noted by 

 Christ, is to be remembered as against the statements commonly embodied in the 

 literature, where it is usually assumed to be constant. 



If these facts be considered, with a mind as free from bias as if no phylum of Ferns 

 existed other than those under discussion, the natural inference would be that they 

 illustrate the origin of a new and efficient protective organ, viz. the '"'■ indusium inferumP 

 •When the further facts are recalled that in Gleichetiia pectinata, Lophosoria and Metaxya 

 no dermal scales are present on the vegetative organs but only hairs, while in Alsophila., 

 Heniitelia., and Cyathea profuse protective scales cover the young stem and leaf — (pre- 

 sumably the result of lateral extension or possibly webbing of the more primitive hairs) — 

 the further inference would be drawn that the hairs, already seen to be present round 

 the base of the receptacle in Lophosoria, Metaxya, and Alsophila, had sometimes in 

 1 Van Rosenburgh [Malayan Ferris, p. 29) specifies in his diagnosis ol Alsophila, "Indusium 

 wanting or spurious and minute, and then consisting of a semiorbicular, inferior, lateral scale placed 

 at the inner side, or of a circular, entire or lobed scale, or a whorl of fibres with the receptacle in the 

 centre." He specifies this particularly for A. glauca J. Sm. Perhaps it was such facts that led 

 Copeland to include all Asiatic species oi Alsophila and Heniitelia under Cyathea. 



