CHAPTER XXXVI 



HYPOLEPIS, ETC. 



In Volume II, Chapter xxx, the Dennstaedtiinae have been described as a 

 specialised Sub-Family of the Dicksoniaceae. Their creeping habit, their 

 long-stalked and usually finely divided leaves with open venation, their 

 solenostelic vascular structure, sometimes polycyclic (Figs. 536-538, Vol. Il), 

 the origin of the leaf-trace often undivided {Dennstaedtid), but sometimes 

 breaking up early into segments (Fig. 581, 

 compare also Vol. 11, Fig, 538), together 

 with their dermal hairs and the absence of 

 scales, except in Saccoloma, are all features 

 of the vegetative system that compare es- 

 pecially with those of Thyrsopteris and 

 Cibotmm. The marginal position of the 

 two-lipped sorus with its prevalent gradate 

 sequence of the sporangia also points in 

 the same direction. But certain species of rig. 581. Transverse section of the petiole 



Microhpia and DeJinstaedtia have h^^x^ ^^ Saccoloma elegans {y, ^,). ^\^q ^^%zv\^x 



^ . strands are black, the sclerenchy ma dotted: 



found to show a departure from the strict the dear areas are ventilated parenchyma, 



basipetal sequence of the sporangia, and connecting with the pneumathodes, /, /. 

 this is accompanied by some degree of flattening of the receptacle (Figs. 

 539> 540. Vol. II). The indusial flaps are unequal, the upper showing a ten- 

 dency to merge into the general expanse of the lamina, while there are also 

 steps towards a lateral linkage of the receptacles into a continuous chain 

 {Saccoloma, Fig. 541, Vol. II). It was, however, noted that Hypolepis shows 

 still more marked features of advance in the sorus; but the details of this 

 interesting genus were held over to this volume : for it was thought that they 

 would form a fitting introduction to the study of those of the Marginales 

 which may be regarded as derivative phyletically from the Dicksonioid type. 

 Hypolepis has in' fact been selected as a favourable example for illustrating 

 a source of those later transitions which a wide comparison of Ferns brings 

 into view. 



The genus Hypolepis Bernh. comprises 29 species, some of which have 

 passed under various generic designations, such as Lonchitis, Chedanthes, 

 Adiantitm, Phegopteris, and Dicksonia. This wide synonymy at once arouses 

 interest, and suggests that it may be a synthetic or transitional type. It has 

 been variously treated by systematists. Presl {Tentamen, p. 161) places it 

 with Lonchitis, and close to Cheilanthes. Hooker {Syn. Filic. p. 128) assigns 



D. H. HILL LIBRARY 

 Ki *i. r - r/^ ;-ia <;tate rolleae 



