i84 ■ BLECHNOID FERNS . [CH 



and B. brasiliense is seen to be extremely close (compare Studies IV, PI. XXV, 

 Fig. 12, and PI. XXX, Fig. 27). 



A further line of comparison may be drawn from the apical region of the sporophylls in 

 Doodia and Woodwardia. In the former the "sori," or rather the fragments of the coeno- 

 sorus, are frequently disposed not in one but in two rows on each side of the mid-rib, the 

 one nearer, the other farther removed from it. Where the sori are placed alternately it 

 would be possible to regard them as fragments of a single Blechnoid coenosorus, each 

 alternate one being removed farther from the mid-rib. But this simple suggestion will not 

 explain all the facts ; for, as Mettenius showed {Fil. Hort. Lips. PL vi, Fig. 5), the sori of 

 the outer row may be superposed on those of the inner, while in D. dives Kze. an incom- 

 plete third row may occur {I.e. p. 66). It seems more probable that with a widening leaf- 

 surface additional sori may be initiated de novo. Such duplication has probably occurred 

 also elsewhere on a broadening leaf-surface, particularly in Diyopteris and Polypodiuin. 



On the other hand, evidence bearing upon the hypothetical disruption can be gathered 

 from the apical region of many fertile leaves and pinnae : and particularly in D. caudatai 

 where the tip is prolonged and entire. Here, while the coenosori are disrupted below, they 

 become continuous for long distances upwards: thus they appear to reconstruct in the 

 simpler distal region the probable source from which the more complicated state originated. 

 This is seen also in Woodwardia, and with remarkable clearness in a species from Hong- 

 Kong, described by Sir W. Hooker as W. Harlandii {Sp. Fil. Vol. ill, p. 71). He tells how 

 the oblong sori become confluent distally as a continuous chain close to the mid-rib, and 

 frequently "sending out nearly opposite pairs of sori even where there is no distinct costule." 

 This condition appears in the photograph from a specimen in the Kew herbarium (Fig. 705). 

 It links readily with Mettenius' drawing of the bipinnate W. viro^inica, though the latter 

 displays a more advanced state of disruption than W. Ha7'landii {Fil. Hort. Lips, vi, 

 Figs. I, 2). The comparison of these species with the simply pinnate leaf of W. blechnoides 

 (Mettenius, I.e. Figs. 3, 4) at once suggests that the state seen in W. Harlandii is con- 

 nected with the extent of the leaf-expanse. Similar details confirming that relation are 

 shown iox Blechnumfraxineum Willd., in Fig. 701, 20 d-f. 



The last-named species has leathery leaves bearing few pinnae : its normal Fu-BlechmaiL 

 type of pinna is seen in {d). Such pinnae appear successively smaller towards the distal end 

 of the leaf {e) : a few imperfectly formed pinnae are seen at the base of the terminal lobe : 

 the last of them are represented only by outward archings of the coenosori, each opposite 

 to the departure of a lateral vein from the mid-rib {e, i-vi). It may be a question whether 

 these represent nascent or decadent pinnae, perhaps the latter : in which case the outward 

 archings seen in B. fraxineicin would be the expression of an ancestral tendency to pinnation 

 imperfectly carried out at the distal leaf-tip, and the relation of the veins to them would 

 be held as defining their pinna-character. But other developments exist where archings of 

 the coenosorus arise between the veins, and in no definite relation to them. These are 

 seen particularly in Blechnitm punctulatum var. Krebsii, as they have also been noted in 

 W. Harlattdii by Sir W. Hooker. The latter have no obvious relation to pinnae. Both 

 types of arching of the coenosori appear in leaves of broad expanse, and it is probably 

 correct to see in the archings of both types a mode of extension of the coenosorus in rela- 

 tion to an expanded rather than merely a condensed leaf-area. 



The irregularities of the coenosorus described in the preceding paragraphs 

 demonstrate it as an entity, which is subject to modifications where a wide 

 leaf-expanse is present. The examples cited taken from three distinct genera 

 suggest that in the Blechnoid affinity a disintegration of the fusion sorus 



