XII] 



SORAL FUSIONS 



229 



have sprung from some type like that of the genus Matteiiccia, where the 

 sporophyll is narrow, bearing on either side of the midrib a superficial row 

 of separate, non-indusiate sori, protected by the strongly recurved margins 

 of the narrow pinnae (Fig. 226). In the simpler types oi Blechrmin represented 

 by the old genus Loniaria the leaves are dimorphic, and the sporophylls 

 narrow as in Matteiiccia. The sori are linked together to form an intra- 

 marginal chain, with continuous vascular supply below the receptacle, 



A B 



Fig. 226. Development of the sorus of Matleitciia rnienneciia. A, B, D, vertical 

 sections through the pinna-margin, showing successive stages of the superficial, gradate 

 sorus, protected by the curved margin. C, a section parallel to the margin traversing a 

 succession of the distinct, non-indusiate sori. ( x 125.) 



Fig. 227. Bkchnum longifolium ( x 3), showing therelationof thefusion-sorus 

 to the venation, and its protection by a continuous "indusium" which is 

 phyletically the leaf-margin. The expanded leaf-surface is a new formation, 

 increasing the photo-synthetic area. 



resulting from commissures which connect the veins laterally together. The 

 whole o{ edichft^sion-sorus is covered by the incurved margin, which acts as 

 an indusial protection. In the more complex types constituting the old genus 

 Bleckmim, but now included in Eu-BlecJmwn, the fusion-sorus is constituted 

 as before, but an extra growth has arisen from the convex adaxial surface, 

 in the form of a flange supplied with vascular strands, and forming a wide 

 and efficient, but secondary photo-synthetic area (Fig. 227). The physiological 



