XLix] SUPERFICIAL DERIVATIVES 279 



commissure, and the Blechnoid type results, as in B. tabidarc or capense, the 

 habit and anatomy of which are closely similar to those of Matteuccia. All 

 of these Ferns are of coarse and xerophytic habit. They suggest the origin 

 of the Blechnoid Series, which forms a prominent feature in the Southern 

 Hemisphere, and particularly in Polynesia (Chapter XLIV). 



The large genus Blcc/muvi,\\n\h. its linear coenosori, introduced several new 

 and peculiar features, leading finally to states parallel with, but phyletically 

 distinct from those of the Nephrodioid Ferns. The most marked external 

 feature is the origin of the longitudinal "flanges," right and left, along the lines 

 of greatest curvature of the reflexed pinnae. These assume, by gradual steps 

 illustrated by specific comparison, a vascular system of their own, and a 

 definite photosynthetic structure: in fact they become substitutionary laminar 

 flaps, but in point of descent they are new structures (p. 165). The sori 

 originally gradate become mixed: the receptacle is flattened, and tends in 

 some derivatives to spread widely over the lower surface: in this a climax is 

 reached in Stenochlaena and Brainea: in the latter the falsely indusial leaf- 

 margin is abortive, and a fully Acrostichoid condition is reached. All this 

 happened without any true indusium being present at all: all the protective 

 flaps are specialised leaf-margins. 



On the other hand, the coenosori may be interrupted, breaking up into 

 short lengths not necessarily corresponding to the original sori. Each is 

 covered by a short length of the "false" indusium. This is seen normally in 

 Woodwardia and Doodia: sometimes on a widening pinna more than one row 

 of them may be seen on either side of the mid-rib. A still more remarkable 

 result appears in Blechmivi pnnctidatum Sw. van Krebsii Kze. Here with a 

 widening fertile pinna, the coenosorus shows varying states of sinuous 

 curvature outwards towards the margin, and of interruptions at the points of 

 strongest curvature, leaving portions of the coenosorus facing one another in 

 the characteristic manner o{ PJiyliitis (^Scolopendriuiii). The anatomy as well 

 as the gradual intermediate steps show that this is the true interpretation of 

 Phyllitis. Consequently this genus is not immediately related to Asplenium, 

 which has been traced from a Nephrodioid source (pp. 192-198). 



In the preceding paragraphs the Cyatheoid, Nephrodioid, and Blechnoid 

 Ferns have all been traced from a superficial origin such as the Gleicheniaceae 

 afford, with Lophosoria as an illustrative connecting link. But Metaxya, the 

 other genus of the Proto-Cyatheaceae, was left aside. The mechanical dead- 

 lock of the advanced Gleicheniaceous sorus was resolved in Metaxya by 

 spreading the flattened receptacle out along the surface of the vein, but 

 without any gradate sequence. Here again the sporangia, though numerous, 

 arise simultaneously: thus technically it is still one of the Simplices 

 (Chapter XLVl). Metaxya is a creeping Fern with solenostelic structure and 

 undivided leaf-trace, and it bears hairs, but no scales. The sporangia have 



