I02 DRYOPTEROID FERNS [CH. 



a vein near to its ending, and consists of a circular receptacle bearing 

 sporangia distally, but not many of them. Its base is surrounded by an in- 

 dusium in the form of a more or less complete ring. In some species 

 (^Physematinni) the indusium appears as a complete covering, separating 

 later into ribbons: in others i^Eu-Woodsid) it appears from the first as 



Fig. 647. I, W. ilveusis, quite young S(5rus, with sporangium {sp), and indusial hair (?). 

 2, W. ilvensis, later stage, with sporangia {sp) and indusial hairs (/, /). 3, ditto, older. 

 4, W. obtiisa, very young receptacle. 5, ditto, with sporangia (sp) surrounded by the 

 ring-like indusium. 6, ditto, older stage, with sporangia {sp) and indusium [i, i). 

 7, W. ihensis, mature indusium: 16/= leaf-margin. 8, W. obitisa, mature indusium 

 and leaf- margin {bl). (After Schlumberger.) 



narrow segments. The sporangia have a stalk composed of three rows of 

 cells, and an apparently vertical annulus, interrupted at the insertion of the 

 stalk, and with the stomium horizontal. In fact they are essentially of the 

 same type as in Dryopteris filix-mas. 



A special interest lies in the development of the sorus, which has been de- 

 scribed by Schlumberger (/.c.p.407; Fig. 647). He tells how in VV.obtiisa (5,6,8) 



