112 DRYOPTEROID FERNS [CH. 



In Chapter XXXIII the Cyatheaceae have been examined comparatively, and 

 their place assigned as further steps in the progression of Ferns still retaining 

 consistently the superficial position of the sori ; but showing an advance to 

 a gradate state, thereby resolving the difficulty of a mechanical dead-lock 

 of a crowded sorus. A basal indusium, partial in Hemitelia and circular in 

 Cyathea, afforded the protection that was lacking in Gleichenia, Lophosoria 

 and AlsopJiila: but in none of these was the step to a mixed sorus taken. 

 It is here that the indusiate Woodsieae come in by supplying this further 

 sign of soral advance, viz. a mixed state: and it is found to go along with 

 other features that indicate a progression towards a Dryopteroid type, where 

 a mixed and indusiate sorus of superficial position is a leading character. 



Of the four genera of the Woodsieae above described that which shows the 

 most primitive characters, indicating for it a near relation to the Cyatheaceae, 

 is Woodsia. This genus may be regarded as comprising small arctic and 

 alpine representatives of the type of Cyathea itself The upright habit, chaffy 

 scales, the pinnation of the leaves — doubly pinnate in some Mexican and 

 Andean species — the open venation, and the basal sometimes continuously 

 ring-like indusium, together with the signs of a gradate sequence of the 

 sporangia, all support the comparison. The vascular system is, it is true, 

 relatively simple: but its dictyostelic structure and divided leaf-trace are 

 just such features as might be expected in a Cyatheoid type of small size. 

 The gametophyte also lends evidence, the most cogent fact being the 

 divided cap-cell of the antheridium in W. obtiisa\ while a division has 

 occasionally been seen also in W. ilvcnsis. These are points of comparative 

 importance in view of the absence of such divisions in advanced Lepto- 

 sporangiate Ferns, and their constant presence in the Cyatheaceae. The 

 convergence of these lines of comparison gives Woodsia a confirmed 

 position in relation to Cyathea, a relationship suggested by earlier waiters, 

 and now supported by detailed facts to which they could not have had 

 access. 



Hypoderris shows advance on Woodsia in various features : but there is 

 no reason to doubt the real relationship. It was suggested by Robert Brown 

 thus {Misc. Bot. Works, Vol. II, p. 543, 1830): "Among the genera of 

 Polypodiaceae having an indusium one remarkable example occurs in a 

 genus as yet undescribed {Hypoderris),\vh.\ch. with an indusium not materially 

 different from that of Woodsia has exactly the habit of Aspidium trifoliatuiny 

 The habit may be held as adaptive to growth in moist tropical shade: the 

 real interest lies rather in the vascular and soral advance. The lax dictyostele 

 of Hypoderris shows perforations as well as foliar gaps, while the leaf-trace 

 is more highly divided than that of Woodsia. These changes are probably 

 concomitant on the habit, and on the fleshy nature of the rhizome. But in 

 the sorus, while the character of the basal indusium is retained, the receptacle 



