ON THE STRUCTURE AND AFFINITIES OF METACLEPSYDROPSIS DUPLEX. 179 
groups of sporangia occur in the same sections as contain the petioles and pinnz 
of the plant. In the absence of evidence of continuity, however, it would not be 
safe to connect the two. 
HisToLtocy oF THE Root. 
The root-trace is very similar to that of Diplolabis rémeri (Solms) ; it is barrel- 
shaped and consists of reticulately thickened tracheides. There are two protoxylem 
groups of scalariform elements situated one at each end of the barrel-shaped trace. 
In one specimen a rootlet seems to be given off from the main trace, but it is very 
much crushed, and one cannot determine whether the smaller rootlets were similar to 
the large ones. Another specimen curved upwards at first, but ultimately turned and 
grew in the opposite direction to that in which a petiole-trace was emitted. Very few 
root-traces were discovered, and of these only the xylem was preserved. 
CoMPARISON WITH OTHER SPECIES. 
In their memoir on the fossil Osmundaceze, Kipston and Gwynne-VauGHAN have 
divided the Zygopterideze into three great groups, and, although few stems belonging 
to this family are known, at least one of the recorded specimens belongs to each group. 
Ankyropteris corrugata (Williamson), A. Brongniart: (Renault), and probably 4. 
scandens (Stenzel) belong to the first group; Diplolabis romerz (Solms) and Meta- 
clepsydropsis duplex (Williamson) to the second; and tapteris di-upsilon 
(Zygopteris Gray) (Williamson) to the third. The stele of the stem in all of these 
species is either circular or roughly stellate in transverse section. When examined 
in detail, however, there are considerable differences between them. 
In comparing the newly discovered stem of Metaclepsydropsis duplex with the 
others, we shall begin with the sémplest known type (it is also the oldest known type), 
Diplolabis rémeri. This latter species has been recorded from the same locality as 
‘M. duplex, viz. Pettycur, as well as from other localities in France and Germany 
where M. duplex does not occur. In it the stem xylem is circular in transverse 
section and consists of two kinds of tracheides, both of which have reticulate thickenings 
on their walls. The xylem elements are arranged in two zones, the inner of which 
contains only short, square-ended tracheides, while the elements of the outer zone 
are long and pointed. The inner tracheides are smaller in diameter than those of the 
outer zone, and they are arranged in vertical series as though they had been derived 
by the septation of long elements. There is no conjunctive parenchyma present in 
the stele. ‘The stem branched dichotomously, and was probably a rhizome. 
The departure of the petiole-trace from the stele is protostelic, and the trace is at 
first elliptical, with sunk protoxylem groups, one near each focus of the ellipse. In the 
TRANS. ROY. SOC. EDIN., VOL, XLVIII. PART I. (NO. 8). 28 
