CH. XLiv] BRAINEA 179 



may be sterile and open : but lower down isolated circular sori are borne on 

 their bifurcated branches : farther down again the veins are connected by 

 arched commissures, which merge into a connected soral line on either side 

 of the mid-rib. Farther back still from the apex, these soral lines may extend 

 outwards from the commissures to form broad Acrostichoid tracts. A section 

 of such a young pinna will appear as in Fig. 702, B: comparison with a like 

 section of Woodwardia ( W) shows how close the similarity is, except for the 

 absence of the indusial flap. 



Fig. 700. A — D — i^oxzxigxd.ol Steiioclilaenasorbi- 

 folia. E = s. sporangium oi Matteiiccia ititermedia 

 for comparison (all x 60). The mark ( x ) on the 

 sporangial stalk indicates the "peripheral" side 

 of the sporangium. As in Diyopteris the other 

 two rows of the three-rowed stalk pass upward to 

 the "central" face. Compare Fig. 657. 



The development of the fertile pinna, as seen in sections of Brainea, shows 

 the usual marginal segmentation (Fig. 701, 19, a). Soon cells project on the 

 lower surface, forming a rounded growth on which sporangia appear, with 

 indications of a gradate sequence {b) : but there is no sign of an indusial flap. 

 Thus the sorus is not restricted peripherally; it spreads towards the margin, 

 following especially the outward course of the veins, and with the ages of 

 the sporangia intermixed ic). Hence it may be concluded that Brainea -is 

 descended from a gradate ancestry with a sorus restricted as in Eu-Blechnum 

 or Woodwardia: and that it has progressed to a mixed condition of the 

 sorus, with Acrostichoid spread towards the margin of the pinna. It is clearl)- 



