XVIl] STIGMARIOPSIS 239 



Calamites. It is noteworthy that the petrified rhizome originally 

 described by Renault as Stigmaria flexuosa, and afterwards 

 identified by him as the subterranean system of Sigillaria 

 Brardi, possesses a vascular cylinder composed of primary xylem 

 strands of crescentic transverse section lining the pith ; a cast 

 of the pith, after the removal by decay of its delicate parenchy- 

 matous tissue, would exhibit the surface-features of Stigmari- 

 opsis. Stigmaria flexuosa no doubt represents a true Stigmari- 

 opsis rhizome. On the other hand, as Williamson has shown, 

 the inner surface of the wood of Stigmaria ficoides consists of 

 a reticulum of xylem with meshes of medullary-ray tissue ; a 

 cast of such a surface presents a very different appearance from 

 that of Stigmariopsis. 



Returning to fig. 209 : from the lower surface of the Stig- 

 mariopsis arms numerous conical outgrowths, reaching a length 

 of several centimetres, project vertically downwards; these also 

 possess Stigmariopsis pith-casts and are identical with the 

 "tap-roots" of Richard Brown. The stump seen in fig. 209 

 shows the characteristic hollow base of the erect stem : this is 

 the region which, it is believed, represents the position of the 

 Stigmarian rhizome from which the aerial shoot was developed. 

 Although no remains of the parent rhizome were found, traces 

 of the rootlets which probably belonged to it were found in the 

 neighbourhood. The absence of the actual rhizome is, however, 

 not surprising as it would not persist after its aerial Sigillarian 

 branches had attained independence by the development of their 

 own dichotomously branched absorbing and holdfast organs. 



The Stigmarian axes of Palaeozoic Lycopods are compared 

 by Miss Thomas' with the prop-roots of certain recent flowering 

 plants which grow in tropical tidal swamps ; their roots grow 

 downwards from the stem at an angle of 50° — 60" before 

 spreading out horizontally. This author also makes some 

 interesting suggestions in regard to the evidence afforded by 

 anatomical structure as to the habitat of Sigillaria and Lepi- 

 dodendron. 



1 Thomas, E. N. (05) p. 187. 



