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MISS NELLIE BANCEOET ON 



occurring in tlie species of Medullosa and in Pteridosperms generally. It is unfortunate 

 that, as mentioned above, nothing is known of the pitting in M. Solmsii, which shows 

 an approach to the South African stem in the more compact nature of the xylem and 

 also in the apparent reduction of "partial pith." 



Steloxylon Jjudwigii, a stem of doubtful Permian age, is another member of the 

 MeduUosean group. It was first somewhat superficially described by Goppert and 

 Stenzel as Medullosa Ludidgii (2, Taf. xvii. figs. 18-20; see also 6, Taf.i. figs. 1-16; 

 and 12, Taf. iii. figs. 6 & 9) ; it exhibits a homogeneous ground-tissue with usually 

 roundish or elliptical steles. Some are, however, considerably elongated and arranged 

 somewhat radially, instead of tangentially as in the case of the plate-rings of Medullosa. 

 The structure of the ground-tissue is not clear, but appears to have been paren- 

 chymatous. The medullary rays of the wood are of varying heights, and are uni- or 

 biseriate, separating groups of two or three series of tracheides. The tracheides bear 

 roundish oval bordered pits in one or more rows. Phloem is not preserved ; while the 

 steles have a partial pith, the structure of which is not clear. Steloxylon Ludwigii 

 differs from the species of Medullosa and from the South African stem in the arrange- 

 ment of the steles. It approaches the new type in the pitting of the tracheides, but 

 differs from it in the less constantly uniseriate nature of the medullary rays and in the 

 definite presence of a partial pith (12, p. 552). 



Sutcliffia insignis, from the Lower Coal Measures of Shore, is considered by Scott (8) 

 to be a probable primitive type of MeduUosean stem. The recent work of Dr. b]. 

 de Praine indicates its aflanities with M. anglica. It possesses a large central stele, very 

 similar in structure to a sins^le stele of M. anglica. Prom the main stele arise subsidiary 



steles at intervals. Phloem is well preserved, and the tracheides usually possess multi- 

 seriate bordered pits. Sutcliffia is not comparable with the South African stem, except 

 through other members of the MeduUosean group. 



Col^oxylon, represented by the species C. ceduense, Brongn., has been described by 

 Eenault as coming from the Permian of Autun (4, pi. 67, figs. 1 & 2). It is in agree- 

 ment with regard to structure with some of the simpler MeduUosese, but it is monostehc 

 for some length of the stem. It is perhaps an aberrant Medullosa ^ and like Sutcliffia is 

 only indirectly comparable with the South African stem. 



The Cladoxylese are a group of forms {Cladoxylon and fdlTcelia) approaching the 

 MeduUosese in the possession of numerous steles. Solms described the structure of 

 (Jladoxylon in 1896 (10) and of Volkelia in 1910 (12). The group differs from the 

 MeduUosese in the arrangement of the steles, which are usually more or less radially 

 disposed (cf. Steloxylon), and also in the minute structure of the wood, the tracheides 

 usuaUy having scalariform pits. The age of the group is Devonian or at least early 

 Palaeozoic. Scott concludes that the Cladoxylese and MeduUosese have no intimate 

 relation, but they probably present a case of paraUel development, showing superficial 

 resemblances to each other in the possession of many steles (8, p. 64 ; 9, p. 497)- 



Cladoxylon Kidsfoni, however, deserves mention on account of an approach in certain 

 characters to the South African fossil. It has been described by Solms-Laubach as 

 coming from the Lower Carboniferous of Berwickshire (12, p. 537). As the stem- 



