630 Pteridophyten. 



The obvious objection to this affinity is the absence of a true in- 

 dusium in Blechnitm ; this difficult}^ has now been obviated by the 

 discovery of Mattencia intermedia C. Christensen, an exindusiate 

 member of the Onocleineae. In this species the sorus of basipetally 

 developed sporangia originates intramarginally and is protected by 

 the recurved margin of the leaf. 



The genus Blechnum as at present usually defined , includes 

 three subgenera. Of these Loynaria is probably the phyletically prior 

 subgenus. Three of the species of this subgenus, B. discolor (Forst.), 

 Keys, B. tabulare (Thunb) Kühn and B. lanceolatum (R. Br.) Sturm 

 are relatively simple as regards the relations of the indusium and 

 the sorus to the margin of the pinna. In the first the indusial Aap 

 originates marginally, but usually intramarginal cells early contribute 

 to its formation; in B. tabulare the indusial flaparises sometimes from 

 a marginal and sometimes from an abaxial cell; in B. laiiceolation 

 the indusium is, in the middle of the pinna at least, formed from 

 a deflected marginal cell, while towards the apex and the base of 

 the pinna it would seem that the indusial Aap arises from the under 

 surface of the pinna and the margin of the leaf is apparently occu- 

 pied by a narrow band, the flange of the pinna. Whereas in these 

 three species there is either no flange or but slight indications of 

 it, B. gibbum (Lab.) Mett. shows within the limits of a Single species 

 a narrow hardly perceptible flange or a wide one forming an assi- 

 milative expansion. B. brasiliense Desv. and B. Fraseri (A. Cunn.) 

 Luerssen, belonging to Eu-Blechnum, have distinctly superficial sori 

 and indusia and a well developed flange provided with vascular 

 tissue; in the second species the flange also has stomata. Of the 

 last subgenus Salpichlaena only one species , B. volubile Klf. was 

 examined; its ontogenetic development could not be studied, but a 

 great Variation in the degree of development of the flange was 

 noted. This structure may be very narrow or a wide assimilative 

 expansion. 



It is contended that in this series of forms we are confronted 

 with a case of phyletic slide of the indusium from a marginal to a 

 superficial position. The indusium is regarded as retaining its iden- 

 tity and representing the "phyletic margin" of the pinna, displaced 

 to the lower surface, while the ostensibly marginal flange is regar- 

 ded as a new organ. It is further contended that there is reason 

 to believe that in the phylogeny this slide of the sori was accom- 

 panied by the appearance, in some cases, of vascular commissures 

 between the veins; that soral development foUowed these extensions 

 "so that the originally isolated sori became threaded together to 

 form continuous lines on either side of the midrib". The resulting 

 sori, or agglomeration of sori, are termed fusion sori of the Blech- 

 mim-type; such sori are clearly not sori in the same sense as the 

 sori of the Cyatheoid or Onocleoid forms. There is strong evidence 

 that in some forms , such as B. boreale, this fusion-sorus may in 

 the phylogenj»- become again disintegrated into separate sori, remi- 

 niscent of the original sori that went to the building up of the 

 fusion-sorus; but there is no reason to believe in an exact cor- 

 respondence between these sori and the original constituents in the 

 phylogeny of the fusion-sorus. It is believed that the sori of the 

 genera Woodwaräia and Doodia have arisen in this vvay from a 

 Blechnoid source by disintegration of a fusion-sorus into isolated 

 portions. Doodia caudata shows a retention of the fusion-sorus on 

 either side of the midrib in the terminal lobe of the fertile frond. 



