42 STUDIES IN FOSSIL BOTANY 



cortex preserved, which they named Myriophylloides. 

 These also were referred by Williamson to his genus 

 Astromyelon. 



The following are the chief characters of Astro- 

 myelon : it has often a persistent pith, though, in the 

 larger specimens, it may have become fistular in the 

 middle. In the specimens first described the pith is of 

 relatively large size. It is surrounded by a ring of 

 bundles, and we shall find there is good evidence that 

 the development of their primary wood was centripetal, 

 not centrifugal as in the stem. In almost all the 

 specimens a thick zone of secondary wood is present. 

 Most often the wood is decorticated, but when the 

 cortex is present it has a very lacunar structure, 

 containing a ring of large intercellular spaces. It is 

 only in very good specimens that the phloem is 

 preserved (see Fig. 15). 



Now some of the smaller specimens, which used to 

 be included in the Myriophylloides of Hick and Cash, 

 have a very different structure from those just described. 

 Some of them have no pith, and the groups of primary 

 wood are very few in number (see Fig. 16). The 

 structure of the cortex, however, is the same in all, and 

 the extreme types are connected by a series of inter- 

 mediate forms. 



Renault, in 1885, expressed his conviction that the 

 French specimens, which he recognised as agreeing with 

 Williamson's genus, were the roots of Calamites (his 

 Arthropitys) and of Calamodendron, and he made out a 

 strong case for his belief. 1 His suggestion, however, 



1 Renault, "Nouvelles Recherches sur le genre Astromyelon," Mem. 

 Soc. Sci. Nat. de Sadne et Loire, 1885. 



