ONOCLEA-WOODSIA SERIES 617 
In the case of Zindsaya 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.’ 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 Cystopterts, 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 Woodsta 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.2 But an examination of their 
sori shows that in Onoclea and Dzacalpe 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 Woodsta and Hypoderris, where also the sori are superficial and 
the indusium basal, the case is different: in Aypoderris 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 
1Tansley and Lulham, Azz. of Bot., xvi., p. 157. 
2 Engler and Prantl, i., 4, p- 159. 
