xxv] 



TUBICAULIS 



435 



plate with the smallest tracheae at each end. The solid xylem 

 of the stem stele (protostele) has peripheral groups of proto- 

 xylem. Nothing is known as to the form of the leaves, but 

 sporangia similar to those of Etapteris (Zygopteris) were found 

 in association with the stem. It is possible, as P. Bertrand 

 suggests, that Renault's species may be the stem of a 

 Tubicaulis. 



Tubicaulis. 



TvhicauUs solenites (Sprengel)\ Fig. 304. 



This species from the Lower Permian of Saxony has been fully 

 described by StenzeP. It is characterised by a very slender 

 erect stem bearing numerous spirally disposed leaves associated 

 with adventitious roots; the single stele (protostele) consists 

 exclusively of tracheae, described as intermediate between the 

 scalariform and reticulate type, surrounded by phloem. Leaf- 

 traces are given off from the periphery of the stele where groups 



Fig. 304. Tubicaulis solenites. (From Tansley, after Stenzel.) Stem and 

 petioles : the latter numbered in the order of their age. 



of smaller elements occur ; these have the form of a wide-open 

 U-shaped strand with the base of the U facing the axis of the 

 stem. As the trace passes out towards the leaves, the ends of 

 the U become more or less incurved. The stem is said to reach 

 ■ Cotta (32) p. 15. " Stenzel (89) Pis. i. ii. 



