XXX] 



DENNSTAEDTIINAE 



73 



which are advanced in various of their structural details, and also in their sori : 

 and that those advances towards lateral linkage of sori, and of transit to the 

 lower surface respectively, are such as point in the direction of those large 

 genera, Nephrolepis, Lindsay a, and Pteris. Here no more can be done than 

 to indicate this as a special interest attaching to the Dennstaedtiinae. 

 They may be held as advanced types from the Dicksonioid affinity, serving 

 as synthetic links with large bodies of Leptosporangiate Ferns. 



But still even in Saccoloina the receptacle is itself truly marginal. It has 

 been found on examination of very young fertile pinnae that the marginal 

 cells give rise, as in all the early Marginales, to the receptacle; while 

 upgrowths from the upper and lower surfaces develope into the indusial 



Fig. 541 . Group of sori, which have become apparently intra-marginal by the upper indusial 

 lip of each fusing with its neighbour, and simulating the rest of the leaf-surface. A = Sacco- 

 lonia elegans. (After von Goebel.) B = Microlepia platyphylla. (Ah&v von Goebel.) 

 C—Neph7-olepis acuta. (After Christ.) D=Nephrolepis cordifolia. (After Christ.) 



flaps, the sporangia arising in a one-sided gradate sequence ("Studies in 

 Phylogeny, \\\" Ann. of Bot. p. 457, Pi. xxxiii, Fig. [6, 1913). It will be 

 shown when the Pterid and Davallioid Ferns are taken up, that these are 

 typically Ferns with a mixed sorus, a condition already faintly foreshadowed 

 by Dennstaedtia and Alicrolepia. Accordingly we shall recognise not by one 

 character only but by several distinct characters that the Gradate Marginales 

 occupy an intermediate place between the marginal Simplices, and certain 

 large families of Ferns which have advanced to a mixed condition of their 

 sori. 



The fifth genus of Prantl's family, viz. Hypokpis, shows still more definite 

 advance not only to a mixed sorus, but to one without any obvious indusial 

 protections: and thus it would rank under the old comprehensive title of 



B. H 18 



