XXXVIII] HISTIOPTERIS 49 



tracts. The ontogeny of the stele has been traced in several sporelings : it 

 illustrates the usual stages (of protostele, medullated protostele, Lindsaya- 

 condition, and solenostele), variously curtailed or lengthened in individual 

 examples. A section above the last leaf-trace which shows no axillary pocket 

 reveals the Lindsay a-?,X.x\XQ.X.wxQ, which is unusually protracted in this Fern 



Fig. 613. Histiopteris incisa (Thunbg.) J. Sm. Trans- 

 verse section of an internode of the rhizome, show ing 

 corrugation of the solenostele. ( x lo.) 



(see Studies VII, Fig. 23). This vascular structure accords with a position of 

 advance on Hypokpis, but it is simpler than in the highly disintegrated 

 Pteridium. Taking all the vegetative characters together, some showing 

 conservatism (vascular structure), others advance (venation and dermal 

 scales), they would suggest that Histiopteris is a probable Dennstaedtioid 

 derivative, holding a position parallel with Pteridium. 



Such comparisons make the question of the soral condition of Histiopteris 

 incisa all the more interesting. The detail of 

 two leaf-segments, in a form where the vena- 

 tion is reticulate, is seen in Fig. 614. The 

 coenosori follow the lateral margins, while 

 the upper indusium appearing as a marginal 

 flap covers the receptacle : there is no lower 

 indusium. The immediate comparative ques- 

 tion will then be as to the relation of the 

 upper mdusium and the receptacle to the mar- j.|„,. Vo feftile leaf-segments en- 

 ginal segmentation. Examination of a large larged. (After Mettenius from Christ.) 

 number of sections has shown some fluctuation in detail. The segmentation of 

 the sterile pinnule is of the usual type : but where the sorus is to be formed 

 the curved outline of the section appears slightly irregular, as seen in trans- 

 verse section (Fig. 615,^,/?), and it becomes difficult to trace the fate of the 

 real margin by its segmentation. Comparison of numerous sections suggests 

 that the receptacle {R), though it often seems as though it were on the lower 

 Bin 4 



