ONOCLEA-WOODSIA SERIES 617 



In the case of Litufsaya the matter is not so clear. The marginal sorus is 

 of the mixed type, but the vascular structure is less advanced than in the 

 Dennstaedtia-Davallia series : it is characterised by possessing in addition to 

 the external phloem-mantle a strand of phloem completely embedded in the 

 xylem. 1 In this, however, there is no serious discrepancy : it appears that 

 the soral and anatomical characters do not always march abreast : in 

 Lindsaya the anatomical advance has lagged behind that of the sorus. 



Lastly, there is abundant evidence to show that an ultimate state of 

 dictyostely has been achieved in the vast majority of the Mixtae : it 

 appears already in Davallia and in Cystopteris, among the series now under 

 discussion. It may be held as a final modification of the solenostelic 

 structure, consequent upon the overlapping of the leaf-gaps. And so it is 

 seen that in the Dennstaedtia-Davallia series the anatomical advance is 

 in the main parallel with that of the soral characters, though exact parallelism 

 is not always maintained. There is thus good reason for holding that the 

 series represents a true line of phyletic advance, leading from the condition 

 of the Gradatae to that of the Mixtae. 



ONOCLEA-WOODSIA SERIES. 



A phyletic line of progression from a basipetal to a mixed sorus, possibly 

 distinct from the last though of much less certainty, may be traced through 

 genera where the sorus is already superficial : viz. from Onoclea and Diacalpe 

 on the one hand to Woodsia and Hypoderris on the other. These genera 

 have been grouped together in most of the leading systems, and are all 

 included under the Woodsieae by Diels.- But an examination of their 

 sori shows that in Onoclea and Diacalpe there is a basipetal succession of 

 the sporangia : this has been demonstrated developmentally in Onoclea, 

 and the result may be summed up in the statement that the sorus is 

 characteristic of the Cyatheae ; but the sporangium is characteristic of the 

 Polypodiaceae, having a long stalk, and the annulus is definitely interrupted 

 at the insertion of the stalk, while there is no regularity of orientation. In 

 Diacalpe as in Sphaeropteris, as well there is also evidence of basipetal 

 succession (see Studies, iv., pp. 55-60). 



But in Woodsia and Hypoderris, where also the sori are superficial and 

 the indusium basal, the case is different : in Hypoderris the sorus is clearly 

 of the mixed type, with flattened receptacle : the same appears to be the 

 case in Woodsia, though the small number of sporangia makes the decision 

 less certain. Full anatomical data are not at hand for comparison, though 

 Onoclea at least appears to have already an advanced type of dictyostele. 

 The evidence, such as it is, appears to indicate that a line of advance from 

 a basipetal to a mixed sorus has existed among the Ferns with superficial 

 sorus and basal indusium, of Cyatheaceous affinity. But these forms require 



^ansley and Lulhani, Ann. of Bot., xvi., p. 157. 

 2 Engler and Prantl, i., 4, p. 159. 



