78 



PTERIDOSPERMEAE 



[CH. 



differ from those of Lyginopteris fronds in the absence of emergences 

 (cf. fig. 404, E). The petioles (fig. 411, B, a) have a single con- 

 centric vascular bundle with internal protoxylem. 



A B 



FIG. 413. Sphenopteris (Diplotmema) elegans. A. Forked rachis with bases of 

 lateral branches (Kidston Coll.); B, pinna. (After Stur.) 



iv. Reproductive organs. 



As yet no satisfactory evidence has been published with regard 

 to the nature of the microsporangia but in all probability these 

 were constructed on the same plan as those of Lyginopteris. 

 There is a strong prima facie case for assigning the seed Sphaero- 

 stoma to Heterangium: absolute proof of organic connexion is 

 still lacking though Dr Benson's recent account of the seeds 



