52 4 FILICALES 



of Hawlea or Angiopteris would readily result from individual growth of 

 the sporangia already initiated. This seems more probable than a fusion 

 of sporangia originally separate, of which there is no structural evidence in 

 the synangia themselves. 



An indirect argument that the synangium was the primitive type is to 

 be found in comparison of the spore-output. It is much larger from the 

 single sporangium of the synangial types, such as Kaulfussia or Ptychocarpus, 

 than from the separate sporangia, such as Angiopteris. It will be shown 

 below that in the Ferns at large a progressive reduction of spore-output 

 from the single sporangium has. accompanied specialisation. If the experience 

 from comparison of other Ferns hold good for the Marattiaceae, then the 

 larger output per sporangium in the synangial types would show them to 

 be the more primitive, while the polysporangiate type with its smaller 

 output would be the more advanced. The question is one incapable of 

 present demonstration, but the comparative and developmental evidence 

 supports the view as stated here. 



In conclusion, it is impossible to avoid the comparison of the Maratti- 

 aceous sorus with the sporangiophores of other Pteridophytes : the vascular 

 stalk or receptacle, the arrangement of the sporangia upon it, the relations 

 of the sporangia, their radial dehiscence all find their correlatives else- 

 where. The chief differences are in the number of the sori, and their 

 position relative to the parts of the shoot which bear them. But in 

 view of the various positions which the sporangiophores hold in the 

 strobiloid Pteridophyta this cannot be held as invalidating the comparison 

 of them with these primitive sori. It may be that the similarity is a 

 result of parallel development; but if that be so, it would still appear 

 probable that the evolutionary progressions which produced them were 

 of a like kind. . It will probably be objected that many of the early Ferns 

 show isolated sporangia of large size, and that this precludes any general 

 application of a primitive soral state for Ferns of the Palaeozoic Period. 

 In reply to this, it may be remarked that the genus Sphenophyllum illustrates 

 how a "monangial" condition may probably arise from an originally soral 

 state. The sporangiophores with four or more sporangia are seen in 

 Cheirostrobbs and in S. majus : and smaller numbers in other species 

 lead to the solitary sporangium of S. Dawsoni (see p. 425). A reduction 

 of like nature is seen in the sori of Gleicheniaceae, and may probably 

 explain also the solitary sporangia of the Schizaeaceae, as indicated by 

 Prantl. Senftenbergia is itself an early example (Fig. 289 A). These early 

 forms must be given full consideration in elucidating the Fossils : they 

 indicate the probability that in early Pteridophytes a monangial state 

 may have been derived from a polysporangiate sorus or sporangiophore. 



ANATOMY. 



. The vascular system of the shoot in certain of the Marattiaceae is 

 well known to be among the most complicated of all the Pteridophytes. 



