XL] WOODSIA 103 



a group of epidermal cells surrounding the nascent receptacle arises as a 

 single-layered ring, but open on the side next the leaf-margin: later some 

 "indusial hairs" fill the gap, and these and the ring form lobes fringed with 

 glandular hairs (s). Thus the indusium is here lobed from the first. In 

 IV. ilvensis the segregation ("auflosung," from his point of view) into single 

 hairs is more advanced (7) : the sorus is initiated by the upgrowth of one or 

 two epidermal cells which form sporangia {sp): later small upgrowths from 

 the leaf-surface (z, /), on the side away from the leaf-margin, give rise to the 

 indusial hairs: others are later formed on the marginal side, and thus the 

 sporangia are surrounded by a ring: but it is open at first on the marginal 



\ 



'i-. 



Fig. 648. Vertical section through a sorus of 

 IVoodsia obtusa, showing .the vascular supply 

 into the receptacle, the basal indusium, and 

 indications of a basipetal succession of the 

 sporangia, (x too.) 



side (i, 2, 7). The receptacle in IVoodsia remains flat, and there is only a 

 slight indication of a gradate sequence of the sporangia: this is natural 

 enough where the sporangia are few. But a basipetal sequence is clearly 

 seen in a vertical section of a sorus approaching maturity (Fig. 648). No 

 evidence of interpolation of sporangia has been obtained in IVoodsia, which 

 thus takes its place as one of the gradate, but with a very short sequence 

 of sporangia. 



The account of the sorus here given follows the verbal description of 

 S. Schlumberger, who regarded the indusium of IVoodsia as in course of 

 dissolution ("auflosung") into constituent hairs. In the comparison which 

 follows later the converse view is taken, viz. that IVoodsia illustrates the 

 upgrade origin of a cup-like indusium from constituent hairs. 



