286 CONIFERALES INCEKTAE SEDIS [CH. 



in French Permian rocks, expressed the opinion that the casts 

 belonged to Walchia stems. In this connexion it is noteworthy 

 that shoots of Voltzia^ also possess medullary casts (fig. 748, A, B) 

 with the superficial features of Schizodendron. Though we have 

 no proof of a connexion between casts and leaf-bearing branches, 

 it is probable that some forms of Schizodendron represent the pith- 

 casts of Walchia : if this view is correct it afiords another argument 

 in favour of connecting Walchia with the Araucarineae, but how 

 close the connexion is cannot be definitely settled without further 

 evidence as to the reproductive shoots. 



Schizodendron, though not confined to Permian rocks, is most 

 abundant in beds of that age ; it is recorded from several localities 

 in Germany^, from France, Russia^, and Canada while the British 

 specimen, though presumably from Enghsh rocks, was not found 

 in situ. 



HAPALOXYLON. Renault. 



Renault* instituted this genus for a cylindrical stem 2 cm. in 

 diameter from the Permian of Autun characterised especially by 

 the parenchymatous structure of the secondary xylem. The 

 type-species, Hapaloxylon Rochei, resembles Araucarites valda- 

 jolensis, a Permian species founded by Mougeot, in its spirally 

 disposed leaf-scars each with an elongated groove marking the 

 position of the leaf-trace. The solid parenchymatous pith is 

 surrounded by a narrow zone of 2 — 3 layers of tracheids with a 

 single row of bordered pits which Renault speaks of as primary 

 xylem : this forms the inner edge of a broad cylinder of homogene- 

 ous parenchyma traversed by uniseriate medullary rays 1 — 3 cells 

 deep. The secondary-xylem elements are rectangular 7 — 8 times 

 as long as broad and without pits. Beyond the cambium is a 

 broad zone of secondary phloem consisting of a regular alternation 

 of well preserved sieve-tubes with lateral sieve-plates and paren- 

 chyma. The cortex contains some secretory sacs and is bounded 

 by periderm. 



The inference drawn by Renault is that the leaves were small 

 like those of Walchia and each had a single vein. There is, 



1 Seward (90). = Weiss, C. E. (72); (74); Potonie (88); (93) A. etc. 



3 Schmalhausen (87) PI. vn. fig. 34. 



' Renault (96) A. p. 360; (93) A. PI. Lxx\a. 



