THE STRUCTURE AND AFFINITIES OF DIPLOLABIS ROMERI (SOLMS). 727 



or two examples have been found in continuity with the stem. A typical transverse 

 section is shown in PL IV. fig. 49 ; it consists of an elliptical mass of xylem with a 

 protoxylem group at each end. Like the xylem of the stem and petiole, that of the 

 root consists of scalariform and reticulate tracheides, the former occurring in the pro- 

 toxylem groups. As has been pointed out, when considering the histology of the stem, 

 these roots appear to rise irregularly and not in definite rows. 



Root-like bodies were also noted as occurring near the base of the petioles. Un- 

 fortunately, the sections showing these somewhat peculiar traces in this position pass 

 through the petiole transversely, and therefore through these traces longitudinally. 

 They did not extend for any distance, and so all that can be stated with confidence at 

 present is that they were certainly not normal pinna-traces. On the other hand, they 

 may not have been roots, but bundles supplying outgrowths of the petiole base just as 

 similar bundles pass out higher up at the pinna-trace departures to supply aphlebise. 

 Further evidence, however, is necessary, and this evidence may be supplied in the 

 future when well-petrified specimens of the stem are discovered. The locality at 

 Pettycur House may possibly yield such examples. 



Summary. 



The stem of Diplolabis romeri is circular in transverse section, and consists of 

 xylem without any conjunctive parenchyma. The xylem is aggregated into an inner 

 zone of short tracheides and an outer zone of long tracheides. The internodes are long 

 and the stem is frequently branched. 



The petiole-trace is at first elliptical, with two sunk protoxylem groups, but it 

 rapidly elongates until it resembles that of Clepsydropsis in shape. Further up the 

 petiole, the trace is similar to that of Zygopteris ; but, still higher up, it assumes the 

 form of the normal Diplolabis petiole-trace. 



The root-traces are barrel-shaped, or elliptical, with a peripheral protoxylem group at 

 each end, i.e. they are diarch. 



The cortex is not generally well preserved except in the petiole. Two regions may 

 be distinguished in this tissue, an inner and an outer. The outer zone in the petiole is 

 sclerotic towards the periphery. In the stem cortex, however, there is no evidence of 

 sclerenchyma. 



Diplolabis, B. Renault, 1896. 

 The characters of the genus are those of its only species, D. romeri. 



Diplolabis romeri (Solms). 



1892. Zygopteris romeri, Solms, " Ueber d. in d. Kalks. d. Kulm v. Glatzisch-Falkenberg in S. erhalt. 



Strukturb. Pflanzenreste," Botun. Zeitung, vol. 1, 1892. 

 1896. Diplolabis esnostensis, B. Renault, "Bass, houil. et perm. dAutun et d'Epinac " (fig. 11 a 14, 



pp. 17 et 18). 

 TRANS. ROY. SOC. EDIN., VOL. XLVII. PART IV. (XO. 24). 107 



