272 SUMMARY OF RESULTS [ch. 



surface, would result in Christensenia, a Fern showing adaptation to forest 

 shade (Fig. 392, B, D, E). These Marattiaceae, however interesting thus 

 for comparison, appear to be a blind branch phyletically, without further 

 derivatives. Nevertheless the comparison of their living sporophylls illu- 

 minates the progression from marginal to superficial sori. 



While the Osmundaceae, which date back to the Permian Period, also 

 appear to bridge the distinction between Marginales and Siiperficiales, there 

 are two other great series of known antiquity; the one strictly Marginal, 

 the Schizaeaceae; the other strictly Superficial, the Gleicheniaceae. The 

 three types thus named probably represent, as nearly as any others that 

 are known, the progenitors of most of the modern Ferns. It is believed 

 that they have remained distinct from Palaeozoic or early Mesosoic time, and 

 represent phyletic lines that were pursued apart throughout the intervening ages 

 (see Vol. II, p. 231, and also its Preface). 



The Schizaeaceae (Chapter XXll) are signalised by a very variable 

 veo-etative system: on the one hand we see the primitive form and anatomy 

 of Schizaea and Lygodium, on the other the more advanced features of 

 Anemia and JMohria. But they all agree in bearing solitary sporangia of 

 strictly marginal origin. These may be shunted during individual develop- 

 ment to a position more or less distinctly superficial, upon the lower surface: 

 but still they all spring from marginal cells; while a false margin, or in 

 Lygodium certain superficial growths, supply a protection, giving the char- 

 acter of a primitive indusium. 



The Gleicheniaceae on the other hand have a very uniform vegetative 

 system (Chapter XXIV). They are primitive in their anatomy, and have 

 their sporangia grouped in radiate sori, which are markedly superficial, and 

 without any specialised protection whatever. The general type of sorus is 

 that of Corynepteris on the one hand, or o^ Angiopteris on the other, though 

 in the latter it is slightly elongated. The superficial position suggests that 

 there had been an early slide to the surface of the widening blade: that 

 position is here as strictly maintained as the marginal position is in the 

 Schizaeaceae. A minor Family, the Matoniaceae (Chapter XXV), of early 

 Mesozoic origin, shares the soral characters of the Gleicheniaceae; but with 

 advances in anatomy and venation, and it differs in the presence of a 

 unique distal indusium and low spore-output. 



All the Ferns mentioned so far have one feature in common. It is that 

 there is no succession of the sporangia of the single sorus in time of origin : 

 either these are produced solitary (monangialj, or where a plurality of 

 sporangia exists constituting a sorus, they are simultaneous in origin. It 

 is this which defines the Simplices, and it may be regarded as characteristic . 

 of the Ferns of the Palaeozoic Age. Their collective characters have been 

 discussed in Chapter XKVI, together with the question of the phyletic dis- 



