CH. XXX] MEDULLOSA 87 



except in the absence of more trustworthy criteria to make use 

 of so protean a feature as leaf-form as a basis of classification. 

 The name Neuropterideae has been frequently employ^ed for 

 Pteridosperms other than the Lyginopterideae on the ground that 

 the foHage of Medullosa is represented by species assigned to 

 form-genera included in the Neuropterideae. It is, however, 

 preferable to restrict the family-name Neuropterideae to fronds and 

 to speak of the second family of Pteridosperms as the Medulloseae, 

 including the genera Medullosa, Sutcliffia, and Rhexoxylon. 



MEDULLOSA. 



Some species of Medullosa probably resembled in habit Angio- 

 pteris evecta and the larger Marattias ; they had short and relatively 

 thick stems clothed with the large decurrent bases of long com- 

 pound fronds superficially like those of some recent Ferns and 

 the leaves of the Cycad Bowenia. It is probable that, as Zeiller^ 

 lias pointed out, the fronds of Medullosa and of other Pteridosperms 

 had a greater tendency than those of true Ferns to a dichotomy 

 of the rachis. In other types the stems reached a considerable 

 length and leaves and branches were separated by several feet of 

 bare stem. The large size of the leaf-stalks in proportion to the 

 diameter of the stem as shown by such species as Medullosa 

 anglica and M. Leuckarti (fig. 416) suggests either a short and 

 thick main axis or, in the case of long stems bearing scattered 

 leaves, a plant that supported itself partially at least by a habit 

 of growth comparable with that of tropical Aroids or other lianes. 

 While Medullosa anglica with its contiguous leaf-bases affords 

 an example of the first type, the occurrence of stems of a Permian 

 species, M. stellata, 3J metres long without branches or leaf-scars, 

 suggests the habit of a bane; similarly a specimen of Medullosa 

 Leuckarti in the Chemnitz Museum bearing a few spreading petioles 

 but little narrower than the stem and given off at a wide angle 

 would seem to favour the view that some species were ill adapted 

 to be mechanically self-supporting plants. The longest piece of 

 stem that has come under my notice is a specimen of M. stellata 

 in the Chemnitz Museum reaching a length of nearly 8 metres: 

 some species attained a diameter of about 50 centimetres. 

 1 ZeiUer (05) B. p. 725. 



