424 



PSAEONIEAE 



[CH. 



Ptychopteris is figured by Fontaine and White^ from Virginia as 

 Caulopteris gigantea. 



Position of Psaronius. 



A comparison of Psaronius with the Marattiaceae and other 

 recent ferns leads to the conclusion that, on the whole, the 

 evidence is in favour of the view usually held, namely that 

 this genus is more closely related to the Marattiaceae than to 

 any other recent ferns. It is, however, important not to over- 

 look the differences between Psaronius and recent genera of 

 Marattiaceae, or the resemblances between the extinct genus 

 and the Cyatheaceae. In habit Psaronius agrees closely with 

 recent tree-ferns ; in the vascular system and in the sequence 



Fig. 300. Dicksonia antarctica (half of stem in transverse section): st, stele; 

 s, solerenohyma. 



of events connected with the production of leaf-traces, there are 

 striking resemblances between Psaronius and the Cyatheaceous 

 fern Saccoloma adiantoides (= Dicksonia Plumieri Hook.) as 

 described by Mettenius'^. The piece of stem of Dicksonia 

 antarctica represented in fig. 300 exhibits a fairly close agree- 

 ment with species oi Psaronius, e.g. P.infarctus (fig. 296, A, B). 

 Moreover, the peripheral steles, which Zeiller has shown are 

 confined to the stem and play an important part in the pro- 

 duction of the roots and in the anastomoses with leaf-traces, 



1 Fontaine and White (80) PI. xxxvi.; Zeiller (90) PI. xiv. 



2 Mettenius (65); Tansley (08) p. 8.5. 



