XXXVI] HYPOLEPIS 9 



sporangia. Various ages of them are intermixed, but the section shows that while 

 stalks of old sporangia are grouped towards the centre, the young sporangia 

 are chiefly near to the margin of the receptacle. A median section through 

 a young sorus show^s the oldest sporangium distal upon the convex receptacle, 

 while others may be initiated below (Fig. 584, b). But though the basipetal 

 sequence is thus seen at first, that order is not maintained. The section also 

 shows that both the indusial flaps are superficial in origin, neither of them 

 representing the margin of the pinnule, which is the receptacle itself. In fact 

 the sorus of D. dissecta is of the Dicksonioid type, but with a more advanced 

 state of the "mixed" condition than is seen in D. rubiginosa or in Microlcpia 



Fig. 585. Mature sorus of Hypolepis 

 nigrescens Hk. , cut vertically, show- 

 ing its mixed character, and the 

 absence of the inner indusium. (x 85.) 



Fig. 5S6. Pinnule of Hypolepis ripens 

 (L.) Pr., seen in surface view, (x 10.) 



(Vol. II, Figs. 539, B\ 540). The basipetal sequence is, however, strictly 

 maintained in D. apiifolia (Vol. Ii, Fig. 539, A'). 



The sorus of Hypolepis nigrescens Hk. presents in section a very similar 

 outline to that oiDennstaedtia dissecta ; but the curvature to the lower surface 

 is stronger, and the sorus is more definitely of the mixed type, while the 

 generic character appears in the absence of the inner (abaxial) indusium 

 (Fig. 585). This may readily be interpreted as a more advanced state, deri- 

 vative from that of the Dicksonieae, the absence of the inner indusium being 

 related to the fact that its protection will be no longer needed where the 

 curvature is strong. But in H. repens (L.) Pr., while the upper indusial flap may 



