CYCADOFILICALES 41 



number and diversity of "fern seeds." In the assured cases, the 

 relation of seed to frond varies from seeds suspended on the under 

 surface of unmodified leaves (as in Pecopteris), to seeds in rows on a 

 special rachis (as in Neuropteris), and finally to seeds isolated at the 

 ends of ultimate branchlets (as in Sphenopteris). Beyond these few 

 definite cases there lies the vast assemblage of paleozoic seeds which 

 have constituted several times as many seed genera as frond genera, 

 . which incidentally is another indication of the heterogeneous character 

 of the latter. It is evident, therefore, that there are seeds enough for 

 all the fronds known; and also that the seed habit discovered in one 

 or even several species of a large frond genus need not be imposed 

 upon all the species. At the same time, it is becoming increasingly 

 apparent that large numbers of frond species and of unassigned seeds 

 must belong to Cycadofilicales. 



Kidston's discovery of specimens of Neuropteris heterophylla 

 bearing seeds is the only direct evidence that Neuropteris in general 

 was seed-bearing; and yet the investigations of Grand 'Ehry (43) 

 on the plants of the Coal-measures of France showed such a constant 

 association of definite types of seeds with definite fronds of Neurop- 

 teris that the inference seems justified that the species of Neuropteris 

 in general were seed-bearing plants. Among the better known seeds 

 thus referred are Pachyiesta, sometimes reaching the size of a hen's 

 egg, and Trigonocarpum (one of whose species is probably the seed 

 of Medullosa anglica). In this general characterization the frond 

 genera known as Alethopteris, Odonto pterin, Linopteris, Lonchopteris, 

 etc., are also included. 



Among the Lyginodendron-like forms, the seeds {Lagenostoma 

 Lomaxii) of L. Oldhamium stand as the only direct evidence of the 

 seed-bearing habit; and yet Heterangium and other stem genera with 

 Sphenopteris foliage are evidently so nearly related to Lyginodendron 

 that one can hardly doubt that many of the species of Sphenopteris 

 were seed-bearing. In fact, the genus Sphaerostoma (Conostoma 

 ovale) is in all probability the seed of Heterangium. 



The species of Pecopteris are much more uncertain, and for many 

 reasons no sweeping inference as to the seed-bearing habit of this 

 great frond genus is justified. The single known seed-bearing species 

 (P. Pluckenetii) is said to be an aberrant one in its frond characters. 



