CH. XLiv] DISINTEGRATION OF THE COENOSORUS i8i 



Blechnoid, and ultimately Matteuccioid in its origin : but the progression to 

 the Acrostichoid state has probably been reached along a line quite distinct 

 from that of SteiiocJilaena: for in the latter it is the "flange" that is absent, 

 while in Brainea the indusial flap is abortive. 



Fig. 702. i9 = transverse section of the mid-rib and sori of a pinna of Brainea 

 insignis (Hk.) J. Sm. , where the sori are exposed, there being no indusial flaps. 

 fV=a. similar section of IVoodwardia radicans (L.) Sm., in which indusial flaps 

 are present. ( x 35.) 



Disintegration of the Coenosorus 

 Reasons have been advanced above for holding the linear sori of 

 Blechnum, § Loviaria to be fusion-sori derived from some such hetero- 

 phyllous type as Matteuccia intermedia (p. 173), and that the homophyllous 

 type oi EiL-Blechnnvi resulted from further modification of pinna-structure in 

 harmony with mesophytic surroundings (p. 165). The widening of the leaf- 

 expanse that characterises the latter has frequently been accompanied by 

 disintegration of the linear-fusion-sorus, and displacement of the resulting 

 parts; thus giving the types of Woodwardia and Doodia. A group of smaller 

 genera centering round Phyllitis {Scolopendritcvi) may also be traced to a 

 like source. It has been shown in Studies IV that these Ferns have the 

 Matteuccioid-Blechnoid type of vascular construction: in particular this 

 appears in the stock of B. punctulatuvi var. Krebsii, which itself gives the 

 key to these developments (Fig. 703). Sometimes the disintegration may 

 appear to be such as to resolve the fusion-sorus into the original sori, each 

 seated on its own vein, as in the flattened fertile pinnae of B. capense (L.) 

 Schlecht (Fig. 701, 22): but in most cases the disintegration results in 

 irregular fragments which present no strict relation to the primary veins 

 (Fig. 701, 23), while in others again the fragments are related rather to the 

 commissures than to the primary veins (Fig. 701, 24, 25). 



Fig. 701. Top right-hand drawing (Fig. 18) shows the distal end of a young pinna of Brainea insignis 

 (L.) J. Sm., with venation, and the relation of the non-indusiate sori to it ( x 10). Fig. 19, a-c, sec- 

 tions of pinnae, showing the initial stages of sori resembling those of Blechmtni, but without indusial 

 flap ( X 125). Fig. 20. BlechnuDi fraxi)ieiim Willd. (/=apical region of pinna with venation, showing 

 its relation to the coenosori. ^ = lovver region showing partial pinnae I-VI. /"shows detail of pinna in, 

 under a higher power (</,(? x 2: / x 15). Fig. 21. Portion of a pinna of Blechmim Fraseri Luerss., 

 showing the relation of the venation to the commissure ( x 15). Fig. 22. Part of a pinna of Blechmim 

 capense (L.) Schlecht, showing the transition from the sterile to the fertile state, with disintegration 

 of the coenosorus ( x a). Fig. 23. Apical region of a pinna oi Blechmim spieant (L.) Wither, sliowing 

 venation, and partial disintegration of coenosorus ( x 3). Fig. 24. Part of a pinna of Blechmim 

 cartilagineiim Sw., showing disintegration of the coenosorus (X3). Fig. 25. Woodwardia areolata 

 (L.) Moore, part of a pinna transitional between sterile and fertile, showing vein-fusions, and the 

 indusial flaps here much narrower than in the sterile type ( x 2). 



