FILICES. 163 



Schenk on the other hand takes his stand chiefly on the structure of the 

 vascular bundles, which cannot, he thinks, be reconciled with that of Ferns ; 

 he does not go sufficiently into the argument drawn by Renault from the 

 branching. He is no doubt right in saying that the bundles have the habit 

 of those of Cycadeae, as appears more particularly in the position of the 

 protoxylem on the phloem-side of the xylem. But I am not convinced that 

 there is any special resemblance between them and the bundles of Macro- 

 zamia, as Schenk contends, for in the latter the xylem on the phloem-side is 

 well developed, while it is entirely wanting in Myeloxylon. Collateral 

 bundles also occur, as is well known, in Ophioglosseae and Osmundaceae, 

 nor are they uncommon in the Ferns generally, though it is true that they 

 are usually found only in the weak ramifications of the nerves of the laminae 

 of the leaves. It is therefore quite possible that in the forms from the Coal- 

 measures this structure may have extended downwards as far as the axes 

 of the pinnae and the leaf-stalks ; and in our recent Marattiaceae, according to 

 Holle, the phloem is as a rule more strongly developed on one side in all foliar 

 bundles. The view here indicated, and which requires further investigation, 

 is at variance with one fact only, namely that, as Haberlandt has shown, in 

 ferns with collateral bundles in which the protoxylem and protophloem are 

 in the normal position, the displacement of the former and its approximation 

 to the phloem, which are characteristic of the leaves of Cycadeae and occur 

 also in Myeloxylon, have never been observed. Williamson again, to prove 

 that Myeloxylon is a fern, insists very particularly on the resemblance 

 between it and Angiopteris ; but it appears from the foregoing remarks that 

 this resemblance is confined rather to the general habit, though it must be 

 acknowledged that the English fossils which go under that name do appear 

 from preparations, for which I am indebted to Williamson's kindness, to 

 show deviations in structure and to approach nearer to that of Marattiaceae. 

 The figures too in Williamson give an essentially different position to the 

 fibre-strands. And now while I prefer not to give a decided opinion on the 

 systematic position of the leaf-stalk which we have been considering, because 

 I see that further research is required fully to clear up the facts of the case, 

 I cannot help saying that the connection between the laminae of the leaves 

 of Alethopteris and the leaf-stalks of Myeloxylon cannot well be disputed 

 without crediting Renault with mistakes of observation, such as must not in 

 any case be imputed a priori to so experienced an observer. It is another 

 question whether the leaves thus reconstructed, which resemble fern-leaves 

 and by their structure remind us of the leaves of Cycadeae, should be placed 

 in the one or the other class. We cannot decide this question so long as 

 the fructification of Alethopteridae is unknown. Perhaps neither of the 

 alternatives is right ; we may be dealing perhaps with an intermediate 

 group, and that there have been such groups is becoming more and more 

 probable. The reader should consult the remarks on this point on p. 141. 



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