474 STUDIES IN FOSSIL BOTANY 



name Cycadofilices may be provisionally retained. Some 

 of these very varied forms will now be shortly described. 



Megaloxyleae 



Professor Seward some years ago described the 

 structure of an interesting stem from the Lower Coal- 

 measures of Lancashire, which he made the type of a 

 new genus of Cycadofilices, under the name of Mega- 

 loxylon Scotti} The specimen, which consists of the 

 wood only, is between 4 and 5 cm. in diameter, the 

 central primary wood having a maximum diameter of 

 nearly 2 cm., while the rest is made up of the secondary 

 xylem-zone. The structure bears a general resemblance 

 to that of Heterangium, but differs from the latter genus 

 in several important points. The stem has no pith ; 

 the whole central region of the stele is occupied by the 

 primary wood, which has a very remarkable structure. 

 The greater part, which may be termed the metaxylem, 

 consists of large, usually very short tracheides, often 

 broader than long, interspersed with tracts of thih- 

 walled parenchyma. This tissue is interrupted by large 

 horizontal gaps, probably due to shrinkage, and recalling 

 the appearance of the discoid pith of Cordaites? 



Five large leaf-trace strands are ranged round the 

 periphery of the primary wood. Their arrangement 

 points to a-| phyllotaxis. Each trace is made up of 

 elongated pitted tracheides, separated by vertical rows 

 of short parenchymatous cells. At the extreme out- 



1 A. C. Seward, " Notes on the Binney Collection of Coal-measure 

 Plants," Part ii. Megaloxylon, Proc. Cambridge Phil. Soc. vol. *. 1899, 

 p. 158. 



2 Similar gaps occur in the pith of Pitys anliqua. See below, p. 515. 



