252 GENERA INCERTAE SEDIS [CH. 



For any decision of relationship, not one range of facts only but the whole 

 body of data must be taken into consideration. The opinion quoted above 

 from Christensen as to the relations of Cystopteris, and in particular the 

 identity of the dermal scales with those of Eitdryopteris^ which he notes, 

 may be held as an embodiment of opinion based on external features; and 

 it points definitely to a Dryopteroid affinity. How then does the anatomy 

 accord with this? Schlumberger {Flora, 191 1, Bd. 102, p. 410) has examined 

 the vascular system of Cystopteris, but apparently in young plants, for he finds 

 only a single strand of the leaf-trace, though in other respects the stelar 

 structure is as in the Woodsieae. But Gwynne-Vaughan {New Phyt. IV, 1905, 

 p. 2 1 5) found a dictyostelic structure wath a binary leaf-trace, as in Matteuccia, 

 or in Dryopteris oreopteris. In addition to this he describes for Cystopteris those 

 peculiar involutions well known as existing in Matteuccm, which occur above 

 each leaf-insertion, though here they are on a smaller scale. How far this 

 peculiarity can be held as evidence of affinity is doubtful: none the less it is 

 a common feature in plants alike on other grounds (Vol. I, p. 150). A further 

 point to be noted is the absence of a perispore, though this is characteristically 

 present in the Dryopteroid Ferns. But this peculiarity is shared by Onoclea 

 sensibilis, though in Matteuccia a perispore is recorded as present (Hannig^ 

 Flora, 191 1, Bd. 103, p. 340). 



The prothalli of Cystopteris bear unicellular hairs, not pluricellular as in 

 the Cyatheoid Ferns, and the lid-cell of the antheridia is undivided. They 

 are thus of the standardised Leptosporangiate type, and do not help in the 

 present argument. 



Taking a general view, the balance of evidence appears to be in favour of 

 Cystopteris ranking with the Cyatheoid rather than with the Davallioid 

 derivatives: in fact that it sprang from a superficial ancestry, and with 

 special relation to the Woodsioid and Dryopteroid Ferns. One feature that 

 seems to have weighed more than it should in canvassing such a decision 

 is the initial relation of the sorus to the leaf-margin. We are familiar with 

 the transit of the sorus from the margin to the surface of the leaf, because 

 in so many Ferns the originally marginal position was retained late in the 

 evolutionary history, and evidence of the transit can be seen in several 

 distinct phyla. But its frequent recurrence does not in any way preclude the 

 converse trend. A type of sorus superficial through a long descent may be 

 equally free to move from the surface towards, or may actually attain a 

 marginal position. This may have happened in Cystopteris. With its real 

 affinities still Dryopteroid, its sorus appears to have attained an approximate, 

 or even an actual marginal position secondarily: in which case the natural 

 affinity would still be with Dryopteris, and the Superficial Series. 



