PROTOCALAMITES 37 



is interesting that this Lower Carboniferous species 

 should be the only Calamite so far observed which has 

 centripetal wood. The protoxylem is in the usual 

 position, in or adjacent to the "carinal" canal, but in 

 this case the development of the primary xylem pro- 

 ceeded in both the inward and outward directions, for 

 each bundle possesses a considerable arc of centripetal 



\ / 

 se ( 



Fig. 11. — Cakinritcs (Protocalainitcs) pettycuroisis. Transverse section of the xylem of 

 a vascular bundle in the stem. _/i, fascicular canal ; .r-, secondary wood ; xi, 

 centripetal wood, on the inner side of the canal. X about 140. S. Cull. 1104. 

 (G. T. G.) 



wood on the side of the canal towards the pith (Fig. i I, 

 xi). Dr. Lotsy has suggested to me that a new genus 

 or subgenus, Protocalamitcs, should be founded on this 

 form, and the proposal may be provisionally adopted, 

 but it is possible that when the course of the bundles 

 has been traced the species may prove to belong to 

 Archaeocalamites (p. 70). The significance of the 

 centripetal xylem as a character shared with other 



