XXI] COMPARISON 149 



suggest a position between Polypodiaceae and Eusporangiate Ferns 

 (Campbell). 



The uniformity with which comparison in respect of each of these twelve 

 criteria points to a primitive state for the Osmundaceae is impressive. All 

 the characters indicate a position for the Family intermediate between the 

 Eusporangiate and the Leptosporangiate Ferns. When the further fact is 

 taken into account, that shoots characteristic of the Family in leaf-arrange- 

 ment and stelar structure, and especially in the features of the leaf-trace, 

 are recorded from the Permian Period onwards, the conclusion appears fully 

 justified that the stock is a very ancient one. Its antiquity harmonises with 

 the position thus assigned to it by comparison. The Osmundaceae may 

 therefore be held to, be a synthetic type between Eusporangiate and Lepto- 

 sporangiate Ferns. 



Nevertheless, the type is an isolated one. There is no Family of living 

 Ferns closely related to them: but it is quite possible that as knowledge 

 increases, affinities with other Palaeozoic fossils may be drawn closer than 

 at present recognised. The Palaeontological history indicates an origin from 

 a protostelic ancestry, and the nearest reference would be to the Botryo- 

 pterideae, which the similarity of the position and structure of the sporangia 

 would fully support. Starting from the small and protostelic state seen in 

 Botryopteris or Graniniatopteris , we may by comparison trace the probable 

 steps of stelar elaboration, and mark at the same time its relation to size as 

 conveyed by the diameter of the stele appended to each name. The Permian 

 Zalesskias (7-13 mm.), and Tliauinopteris (ii mm.), were of a fair size: 

 though they retain a solid xylem-core this is differentiated into inner storage 

 xylem, and outer conducting xylem, with protoxylem just as it has been 

 found to be in Diplolabis Romeri by Gordon. The succeeding Jurassic fossils, 

 O. Gibbeana (4"5 mm.), and O. Dunlopi (5 mm.) were smaller, showing 

 dimensions about equal to those of living Osmundaceae, which also they 

 resembled in their structure, being dictyoxylic: but O. Kolbei (20 mm.), 

 referred to the Neocomian, was not only ver}^ much larger, but it is shown 

 to have possessed a dictyoxylic stele with "mixed pith." Unfortunately 

 the state of preservation of the previously named fossils did not allow of 

 examination of their pith-structure. The stelar condition of the Jurassic 

 Osmundaceae corresponds to that of most of the living Osmundaceae, 

 while the state of O. Kolbei is matched by the abnormal state of O. regalis 

 shown in Vol. I, Fig. 120. The next step is seen in O. skidegatensis (24 mm.) 

 of Lower Cretaceous time, a beautifully preserved fossil, showing separate 

 xylic strands, with internal phloem, and incipient dictyostely. This is 

 matched, but without the complete foliar gaps, by the living O. cinnainoviea 

 (4'5 mm.). The difference in size between this species and the large fossil 

 probably accounts for their absence: for in the largest of the fossils. 



