XX] SORT 113 



result comes from the Ophioglossaceae. At first sight this might suggest that 

 the higher numbers are an indication that the synangial types are the more 

 primitive: but for reasons already explained (p. 89) this will not hold for 

 the Ophioglossaceae. It seems not improbable that a biological advantage 

 follows on the synangial state, and this may explain what is apparently the 

 fact, that it has originated along a plurality of evolutionary lines. 



Passing now to the fossil Ferns having fructifications which may be 

 ascribed to a Marattiaceous affinity, many of them have foliage of a 

 Pecopterid type: the segments are relatively narrow, and in none of the 

 earliest are there broad leaf-expanses. The sori are habitually disposed in 

 two intra-marginal rows, one on either side of the midrib. The same 

 arrangement is constant also for the living Marattiaceae, excepting Christen- 

 senia. This relation to the margin is significant for comparison with the 

 Ophioglossaceae, and still more with the Botryopterideae. In both of these 

 the sporangia or sori are actually marginal. Corynepteris is specially pertinent 

 since its sori, so closely resembling those of certain Marattiaceae, neverthe- 

 less appear to be marginal on the very narrow segments (Fig. 405). Kidston 



Fig. 405. A — Corynepteris Essenghi Andrae, from the Carboniferous 

 { Westphalian). Fragment of a fertile pinna. ( x 6.) B—C. coralloides 

 Giitbier, from tlie Westphalian. Fragment of a fertile pinna. ( x 4.) 

 j5' = sorus of the same species seen laterally. ( x 28.) (After Zeiller.) 



remarks (Fossil Plants, Mem. Geol. Survey, Pt. 4, p. 300, 1923), "There can 

 be no doubt that C. coralloides Gutbier sp. belongs to the Zygopterideae." 

 It has been demonstrated in Vol. I, Chapter XII, how frequently in modern 

 Ferns the sorus has slid phyletically from the margin to the surface of an 

 enlarging leaf-area. The facts suggest very strongly that a similar transfer 

 from the margin to the surface has taken place early in the evolution of the 

 Marattiaceae from a narrower-leaved ancestry. All the facts relating to the 

 sporophylls of modern Marattiaceae coincide with such an origin, subject to 

 the sori spreading over an enlarging leaf-area, as explained in the foregoing 

 descriptions of them. Such considerations point to a circular group of a small 

 number of sporangia as constituting an early type of sorus: and this is what 



