476 STUDIES IN FOSSIL BOTANY 



wood reappear in Zalesskya diploxylon, a Permian plant 

 recently described by Kidston and Gwynne-Vaughan, 1 

 and shown by them to be a primitive member of the 

 Osmundaceae. In the Zalesskya, however, there is no 

 xylem-parenchyma, and many other differences forbid 

 the suggestion of affinity. The conversion of the 

 central wood into a water-reservoir, as it became super- 

 fluous for conducting purposes, may well have happened 

 in more than one line of descent (cf. Lepidodendron 

 selaginoides). 



The position of the genus is best denned in the 

 words of its discoverer : — 



" Megaloxylon adds another connecting link between 

 the Palaeozoic Cycadofilices and recent Ferns ; in 

 anatomical characters the two genera Lyginodendron and 

 Heterangium approach most nearly to the Osmundaceae 

 and Gleicheniaceae respectively ; in Megaloxylon, on 

 the other hand, the structure of the primary xylem 

 affords evidence that the Lygodium type of stem was 

 also represented in the Cycad - Fern alliance which 

 played so prominent a part in Palaeozoic vegetation." 2 



A more complete knowledge of the plant will be 

 necessary before its affinities can be determined. 



Calamopityeae 



Calamopitys. — While Megaloxylon recalls in a general 

 way the structure of Heterangium, the plants next to 

 be considered show a. type of anatomy comparable to 

 that of Lyginodendron, though here also the differences 



1 " On the Fossil Osmundaceae," Part ii. Trans. Royal. Soc. Edinburgh, 

 vol. xlvi. Part ii. p. 226, 1908. 



2 Seward, I.e. p. 171. 



