FERNS— FRUCTIFICATIONS 275 



Filicales. The evidence from the fructification, when 

 available, was formerly considered decisive, but we shall 

 find that this is no longer necessarily the case (see p. 

 289) ; anatomical characters, if carefully interpreted, 

 may carry equal weight. 



A few of the chief forms of fructification attributed 

 to Palaeozoic Ferns will now be considered, in relation, 

 where this is possible, to the form and structure of 

 the fronds on which they were borne. Certain special 

 groups, in which our knowledge of the plant as a 

 whole is more complete than usual, will be dealt with 

 later on (Chapter IX.). 



In the majority of cases, fossil fructifications referable 

 to Ferns have been found on specimens preserved as 

 impressions. In favourable instances such specimens 

 may show something of the structure, as well as the' 

 form of the reproductive bodies, for spores and the 

 walls of sporangia usually have more or less cuticu- 

 larised membranes, so that they withstand decay, and 

 may often be found in a recognisable form in the 

 carbonaceous layer coating the surface of the impres- 

 sion. In other cases, again, petrified fructifications 

 have been found, and here, of course, the evidence as 

 to structure is far more satisfactory, though the petrified 

 specimens are usually fragmentary, and hence difficult 

 to correlate with those in which the external characters 

 are shown. 



It has been customary, for some time past, to divide 

 living Ferns into two main series — the Eusporangiatae 

 and the Leptosporangiatae — according to the develop- 

 ment of the sporangium, which arises from a group 

 of cells in the former, and from a single cell in the 



