146 



MEDULLOSEAE 



[CH. 



RHEXOXYLON. Bancroft. 



Rhexoxylon africanum Bancroft. The genus Rhexoxylon was 

 instituted for a new type of stem represented by a single incomplete 

 specimen from the Karroo series of South Africa : its precise 

 geological horizon is not known but it may be referred provisionally 



FIG. 437. Rhexoxylon africanum. Transverse section of stem showing peripheral 

 steles and central (c) stele. (After Bancroft; x 2.) 



to the lower or Palaeozoic portion of the series. Though our 

 knowledge of the morphological features of the type-species is 

 far from complete owing in part to the method of preservation 

 of the specimen and in part to the destruction of the outer portion 



