XII] 



THE PHYLETIC SLIDE 



the sorus in Dennstaedtia punctilobula (Michx.), Moore, is marginal, as it is 

 in Cibotiuiii. The same is the case also in D. dissecta (Svv.), Moore (Fig. 215). 



Fig. 2 [5. a— Pinnule of Dennstaedtia dissecta seen in surface view, showing the marginal sori on the 

 apex of the anadroniic branches of the veins. ( x 4.) <5 = Sorus very young, cut in vertical section, 

 showing the marginal receptacle and superficial indusial flaps. ( x 1 50. ) c= Mature sorus in vertical 

 section. ( x 35.) 



Each sorus is seated on a vein-ending, but 

 liquely downwards id). A vertical section 

 through the mature sorus gives the relation 

 of the indusial flaps to the receptacle in 

 which the vein terminates. As the sorus 

 matures it assumes the mixed character (r). 

 Both the indusia are well developed ; but 

 in the related Hypolepis nigrescens, where 

 the downwards curvature of the whole sorus 

 is more marked, the abaxial indusium is 

 absent: obviously it is not necessary for pro- 

 tective purposes when the strong curvature 

 brings the sorus close to the lower leaf-sur- 

 face, and it is accordingly aborted {Studies, 

 VII, Fig. 38). The case is, however, slightly 

 different in Hypolepis repens, where the pin- 

 nule is broad, and the sorus is seated upon 

 a vein-ending at some distance apparently 

 from the leaf-margin (Figs. 216, 217). In 

 other respects the relation of the parts is 

 as before : but the sorus is more extended 

 along the vein, while the vascular tissue 



when mature it is directed ob- 



Fig. 216. Pinnule oi Hypolepis repens, 

 seen in surface view. ( x lo-) 



reaches beyond the receptacle into the upper indusium; this is now flattened 



