FERNS— SUMMARY 353 



sporangiatae takes a secondary place, and to this the 

 palaeobotanist can make no objection, for on existing 

 evidence it is doubtful whether the distinction existed 

 among Palaeozoic Ferns. 



A remarkable lacuna in our knowledge of the older 

 fossil Filicales is the entire absence, so far as is yet 

 ascertained, of any satisfactory evidence for the exist- 

 ence of heterosporous forms. Fossil Rhizocarps have 

 often been described, but, so far as the earlier strata 

 are concerned, on the most questionable evidence. 



There are strong reasons for supposing that hetero- 

 spory must have appeared among Ferns in Palaeozoic 

 times, but this question will be considered in the last 

 chapter of the book. 



23 



