CHAPTER I 

 CYCADOFILICALES 



The discovery of this paleozoic group of gymnosperms has been 

 one of the remarkable achievements of the present decade. Including, 

 as it does, the most fernUke assemblage of seed plants, the discovery 

 is of enormous importance to phylogeny. A brief sketch of the 

 development of our knowledge of the group will serve as an introduc- 

 tion to the fuller account. 



The Carboniferous period is notable for its fernlike vegetation 

 (ii), which has been estimated (56) to make up at least one-half of 

 the known flora. The classification of the leaves is based upon form 

 and venation, and a number of frond genera have been described, 

 which, although necessarily artificial, are sufficient for the cataloguing 

 of material. The association of sporangia with these fronds is by 

 no means general; in fact, an enumeration (11) of the frond species 

 from the British Carboniferous showed an association of fronds and 

 sporangia in less than one-fifth of them. It was assumed, without 

 question, that the sporangium-bearing fronds must be those of ferns, 

 and the opinion became current that the sporangia indicated that these 

 ferns were of the general Marattia type. Hence there arose the belief 

 that the most dominant vegetation of the Carboniferous could be 

 spoken of as a Marattia plexus, including a far greater diversity of 

 forms over a far wider geographical range than do the Marattiaceae 

 of the present flora. This view involved also the belief that the 

 relative age of eusporangiate and leptosporangiate ferns had been 

 settled by the sure testimony of history. 



In 1883 Stur (7) had become so impressed by the fact that the 

 large majority of the carboniferous fronds remained persistently 

 sterile, in spite of the increasing accumulation of material, that he 

 suggested that these forms might not be ferns. In view of the sub- 

 sequent discoveries, this statement, based only upon persistent nega- 

 tive evidence, appears like a prophecy. However, a few years later 

 (11) sporangia were discovered upon the persistently sterile fronds 

 of a species of one of the largest of the frond genera {Sphenopteris). 



