I50 OSMUND ACEAE [CH. 



O. Cai'nieri (33 mm.), full dictyostel}^ of an Osmundaceous stele with regular 

 foliar gaps is reached, a fact which accompanies, and is perhaps causally 

 related to, its large size. Its stele is seven times the diameter of that in 

 O. cinnamomea (see Fig. 431, p. 142). The march of these successive steps 

 in geological time, together with the progression in size, leaves little doubt 

 as to the stelar story which they convey. The ancient family started from 

 Palaeozoic protostely: it reached its structural and dimensional climax 

 in late Mesozoic time: the living representatives appear to have stood still 

 both in size and in structure at the state attained in Jurassic times, ex- 

 cepting O. cinnavwviea and occasionally Todea hyinenophylloides, which reflect 

 structurally the state of the Cretaceous fossils. The facts, apart from all 

 theory, do not suggest any degradation of structure, such as has been 

 suggested on grounds of purely anatomical comparison without any relation 

 to other lines of enquiry. The living Osmundaceae, when examined in 

 relation to all their features, appear to record in their anatomy steps in an 

 upgrade elaboration of the stele, though the most advanced of those steps 

 were already attained in the Mesozoic Period. Such a conclusion accords 

 with the position assigned to them on general grounds of comparison, as 

 taking an intermediate place between the Eusporangiate and the Lepto- 

 sporangiate Ferns. 



The two (or three) surviving genera of the Osmundaceae suggest in 

 their sporophylls the origin of two different states which have figured 

 conspicuously in the later evolution of the Ferns. Osniimda retains the 

 marginal or approximately marginal position of thesporangia upon its narrow 

 pinnules, which was characteristic of the Botryopterideae: but Todea bears 

 its sporangia superficially upon the lower surface of its broader pinnules. 

 Intermediate states are seen abnormally in Osimcnda (Fig. 420), and these 

 suggest that the superficial position is derivative, and consequent upon an 

 increase in surface of a primitively narrow sporophyll (Vol. I, Chapter Xll). 

 The difiference thus seen between the two living genera may be held to pre- 

 figure two conditions which become stereotyped in distinct phyletic lines. 

 These will subsequently be designated the Marginales and the Super- 

 ficiales. The former is represented among early Ferns by the Schizaeaceae, 

 and the latter by the Gleicheniaceae. But the Osmundaceae, consistently 

 with the position which they hold both in the fossil history and as shown by 

 a comparative study of the Class as a whole, include both types. In this 

 again they appear to be a synthetic Family. 



It will not be necessary to dwell upon the evidence from spore-numbers 

 per sporangium in the Osmundaceae. It puts into actual figures the inter- 

 mediate character of these Ferns between the Eusporangiate and the 

 Leptosporangiate types, with an indication of a more primitive state than 

 in any living Schizaeaceae; but there is an equivalence with some Hymeno- 



