ACROSTICHOID DERIVATIVES 



■A. J_*l I ,^-\ V . I\. 1 / ^ I II I — I 1 I I I I I I 1-4 U' I \ / /\ 1 I \ / I ,' L ' 



133 



receptacle of the sorus itself becomes extended to form an enlar<Ted fertile 

 surface (Fig. 666). In i. {P. articiUatd) the receptacle on either sTde of the 

 mid-rib is narrow: in ii. {P. scandens) it is widened, carrying the leaf-maroin 



, Fig. 664. Leptochilns ciispidatits, after Frau Eva Schumann. 



^ - middle-foi-m between sterile and fertile, with sporangia still 

 unripe. -5 = middle-form with ripe sporangia. ( x about 8.) 



backwards: in iii. {P. osmundaced) this widening is carried farther, so that 

 the leaf-margin appears to arise from the upper surface: in iv. {P. ccrvina) 

 the receptacle appears to occupy the greater part of the upper surface, while 



