134 



DRYOPTEROID FERNS 



[CH. 



the margins appear close together, near to the mid-rib. An indication that 

 this. is a correct interpretation is given by a section in the plane including 

 the course of the vascular supply: such a section (v.) shows the strand as a 

 recurved loop, following the course which the extension is believed to have 

 taken. 



The development in Stenoseinia has been shown by Frau Eva Schumann to 

 be again different, however nearly the end-result may appear to be the same 

 (Fig, 6^'^'). The sporophyll is here greatly contracted compared with the 

 foliage leaf. No chlorophyll-parenchyma is visible. Transverse sections show 



%w^ 



Fig. 665. Leptochibis cuspidaUis. Young sporophyll in 

 transverse section, showing Acrostichoid state. ( x about 

 55. After Frau Eva Schumann.) 





Fig. ^Gd. Various forms of the sori 

 oi Polybotrya. i. — P.articiilata. ii.= 

 P. scandens. iii. = P. osinimdacea. 

 w. — P. cervtna. \. = P. cervina, 

 showing course of venation. (After 

 Frau Eva Schumann.) 



that sporangia are borne both on the lower and on the upper surfaces, 

 though they are less numerous on the latter. When young the actual leaf- 

 margin can be traced structurally between the sporangia {R, Fig. 66d>), so 

 that here there has been no displacement of the margin : the sporangia arise 

 from both surfaces. A comparison with the Pteroid type is not here permissible, 

 for the margin itself does not act as a receptacle, but remains persistently 

 unchanged (Schumann, I.e. p. 253). The conclusion follows that Stenosemia 

 and Polybotrya are rightly placed side by side, but distinct, since they 

 illustrate distinct methods of arriving at practically the same Acrostichoid 

 result. 



