4 o 4 STUDIES IN FOSSIL BOTANY 



cylinder, from which the leaf-traces were given off. 

 The stele differs, however, from that of the other genus 

 in one striking point ; in Heterangium the whole 

 interior of the stele is occupied by the primary wood 



get 



Fig. 155. — Heterangium Criez'ii. Transverse section of stem. x t central mass of 

 primary wood, consisting of tracheides and parenchyma ; .r 2 , secondary wood, 

 beginning to form ; next come phloem and pericycle ; i.c, inner cortex (x in this zone 

 is a sclerotic group); Lt, leaf-traces; r, base of an adventitious root; o.c s outer 

 cortex or hypoderma (only present in places) ; pet, base of petiole, partly detached. 

 X about 5. S. Coll. 396. (G. T. G.) 



(see Figs. 154 and 155), which extends to the centre, 

 leaving no pith whatever, while in Lyginodendron, as 

 we have seen, the large pith is a constant feature. 

 The difference is so striking that it might seem, at 

 first sight, to preclude the idea of any close relationship 

 between the two genera ; yet, as Williamson at once 



