656 GENERAL COMPARISON OF THE FILICALES 



and pectinate^ to the basipetal sorus of Alsophila : the addition of a basal 

 indusium, together with increased vascular complexity, gives the full type 

 of Cyathea. In relation with these genera, though on a minor scale of 

 structure, is probably Onoclea, and as possible last terms leading to the 

 mixed sorus may be Woodsia and Hypoderris. But this line requires more 

 full investigation before it can be accepted with assurance. 



A third line, which is however more certain, is the Matonia- Dipteris 

 series. Again the sori are superficial, and the relation of Matonia is 

 clearly with the Gleicheniaceae. There can be no doubt of the close 

 relation of Dipteris to Matonia, as shown by external form, as well as 

 by anatomy : but in place of the simple sorus of Matonia and of Dipteris 

 Lobbiana that of Dipteris conjugata shows the mixed condition. It seems 

 clear that there has been a direct transition in this case from the simple 

 to the mixed sorus, leading in fact to a form long included in the genus 

 Polypodium but without the intermediate basipetal condition, though this 

 has been found usual in other cases. 



It would thus appear that along several distinct phyletic lines the 

 condition with mixed sori may have been attained. This is the most 

 advanced state of the present day among the Filicales. It will remain 

 for future workers, by anatomical and other enquiry, to disentangle more 

 fully the confused phyletic lines of the Polypodiaceae : the present work 

 will at least have served to show where the tangle actually lies, and 

 some of the probable lines which have led up to it. 



Returning now to the base of the series of the Filicales, as represented 

 in the scheme, it remains to consider what idea can be formed of a 

 primary type for the group. As there is no clear evidence of the nature 

 of the Fern-stock prior to the known types of Simplices, it is only on 

 a basis of comparison of these with one another, and with other early 

 Pteridophytes, that a conception can be formed of the probable origin 

 of the sporophyte in the Filicales. Comparison, checked by the Palaeonto- 

 logical facts as stated at length above, has led to the recognition of the 

 following characters as primitive for Ferns : the shoot consisted of a radial 

 upright stock, showing occasional dichotomy, with protostelic structure, 

 .bearing radially disposed leaves, and supported by adventitious roots: 

 the leaves were primitively flattened, of relatively simple outline, in which 

 dichotomy was a prevalent, but perhaps not an exclusive feature : the 

 leaf-trace consisted of a single strand : the meristems of axis, leaf, and 

 root were not dominated by a single apical cell, but showed a group of 

 initials : all the leaves were potentially sporophylls : the sori were probably 

 definite, marginal or superficial, disposed in a single row on either side 

 of the midrib : the sporangia of each sorus were simultaneous in origin, 

 sessile, and of large size, with high individual output of spores. 



The characters thus summarised indicate an essentially strobiloid type 

 not very much removed from some of those which Palaeophytology has 

 brought to light. Among the Sphenophyllales and Equisetales are forms 



