414 



PSARONIEAE 



[CH, 



is applied to steins exhibiting spirally disposed leaf-scars like 

 those of recent tree-ferns; in Megaphyton the scars are dis- 

 tichously arranged, in two rows, while Ptychopteris is applied 

 to decorticated stems. These terms are used for stems belonging 

 to one generic type and possessing the structure of Psaronius 

 stems. 



The researches of Grand'Eury^ led to the discovery that 

 certain Psaronius stems bore fronds of the Pecopteris type 

 some of which bore sori of the Asterotheca or Scolecopteris type. 

 The same author^ has also contributed many interesting facts, 



Fig. 295. Psaronius stem with roots. (Much reduced. After Grand'Eury.) 



obtained by an examination of the relation of Psaronius stems 

 to the sediments of French Coal-fields in which they occur, 

 in regard to habitat and manner of growth. The specimen 

 represented in fig. 295 shows a portion of a Psaronius stem, the 

 upper part of which illustrates the Caulopteris state of preser- 

 vation, while the lower part is covered by a mass of roots. It 

 is probable, as Rudolph^ suggests, that this rich development of 

 roots, which gives to an old Psaronius stem the appearance of an 



' Ciraiid'Eury (77) A. 

 ^ Budolph (05). 



- Grand'Eury (77) A; (90) A. 



