CLADOXYLEAE 497 



same horizon and locality which yielded the specimens 

 of Calamopitys Saturni, described above. Their age is 

 now considered to be Devonian. They are fragments 

 of stems, referred to several so-called species, but 

 agreeing in the fact that they have a complex, poly- 

 stelic structure. In Cladoxylon mirabile the steles are 

 much elongated, as seen in transverse section, often 

 curved and sometimes fusing with one another, their 

 long axis usually lying in the radial direction. In 

 C. dubium they are shorter and simpler in form. The 

 point of interest is that in most of the specimens each 

 stele has its own zone of secondary wood, while in other 

 cases the primary structure has remained unaltered, 

 thus presenting altogether the appearance of a poly- 

 stelic Fern-stem. Both primary and secondary wood 

 are made up of scalariform tracheides ; the secondary 

 zone is traversed by numerous medullary rays. In the 

 primary wood, one or more groups of spiral elements 

 have been recognised, usually situated (according to the 

 species) at one or both ends of the stele. In one case, 

 an appendage, containing a single concentric bundle, 

 was found in connection with the stem, and was 

 no doubt of the nature of a petiole. The general 

 organisation is clearly comparable to that of a Medullosa, 

 though there are many differences in detail. It is 

 certainly interesting to find, that this remarkable 

 combination of polystelic organisation with secondary 

 growth had already appeared at so ancient a period as 

 that of the Devonian. 



It is not probable that the relation between the 

 Cladoxyleae and the Medulloseae was at all a close one, 

 for the differences in the minute structure of the wood, 



