Medullas a from the Lower Coal Measures . 257 
type shown in the new specimen, in which the transition from primary to 
secondary wood is difficult to trace even when the preservation is good. 
The ‘ partial pith ’ is evidently homologous with the primary wood of 
the stele, but in some of the Chemnitz fossils the proportion of parenchyma 
to wood elements was very different from the new specimen, 1 though in 
some cases poor preservation may account for the seeming difference. 2 So 
Text-fig. 3. Transverse section of star-ring, x 53. xyO = primary wood ; xy . 2 
= secondary wood ; pxy. protoxylem ; st . 1 and st? = portions of two outer steles. 
long ago as 1881 it was pointed out by Goeppert and Stenzel 3 that the 
star-rings differed from the peripheral steles only in size and shape, and this 
observation can clearly be extended to the new Medullosa also. 
Course of the Steles . — The central stele or star-ring shows no change 
in the portion of stem which was available for investigation, so that neither 
its origin nor its ultimate fate could be determined. 
1 Loc. cit., p. 54, Text-fig. 5. 
2 Loc. cit., p. 64, Text-fig. 9. 
Goeppert, H. R., und Stenzel, G. : Die Medulloseae. Eine neue Gruppe der fossilen 
Cycadeen. Kassel, 1881. 
