XXX] MEDULLOSA 109 



In addition to Alethopteris, Neuropteris (including Cyclopteris) 

 and Odontopieris fronds, which are known to possess rachises with 

 the Myeloxylon features, there is reason to beheve that the Permian 

 Gallipteris fronds and possibly some of the older Taeniopteris leaves 

 may also belong to Medullosa^. It is, however, unsafe to assume 

 that the occurrence of Myeloxylon petioles necessarily denotes 

 the existence of Medullosa. The French stem Colpoxylon aeduense 

 Brongn.^ bore leaves with the same general anatomical features 

 as those of a typical Myeloxylon, and there can be httle doubt 

 that other genera of the Medulloseae also possessed fronds con- 

 structed on the same plan as those known to have been borne 

 by Medullosa. An interesting illustration of an injured organ 

 that had produced a wound-cambium is afforded by a Myeloxylon 

 petiole from the Coal Measures described by Mr Holden*. 



Keproductive Organs. 



Reference was made in volume ii. to the reasons which led to 

 the removal of several genera of Carboniferous and Permian 

 fronds from the Filicales to the Pteridosperms, and in Chapter xxix. 

 of the present volume certain species of Sphcnopteris are described 

 as the foliage of Lyginopteris and Heterangium. It is with such 

 genera as Neuropteris, Alethopteris, Linopteris and others that we 

 are now more especially concerned, as they represent some of 

 the types of leaves borne by Medullosa and other members of the 

 Medulloseae. The absence of any specimens among the large 

 number of these common genera bearing undoubted sporangia 

 aroused suspicion as to the correctness of the generally accepted 

 view that these f ern-hke fossils were the leaves of Palaeozoic Ferns. 

 Subsequently the suspicion based on negative evidence was con- 

 firmed by researches into the anatomical structure of the leaf- 

 bases, petioles, and fragments of pinnae attached to and associated 

 with stems of Medullosa. It is only in a few cases that actual 

 organic connexion between reproductive organs and MeduUosan 

 leaves has been demonstrated, but from such facts as are estab- 

 hshed it is safe to make the general statement that stems of 

 Medullosa — a generic term that undoubtedly includes plants. 



1 Weber and Sterzel (96) B. p. 139. ' Page 142. 



» Holden, H. S. (10). 



