KIDSTOX : THE FLORA OF THE CARBONIFEROUS PERIOD. 357 
depressed ring placed about midway between the central single vas- 
cular cicatrice and the outer margin of the scar, Text Fig. 10. The 
rootlets are very long and bifurcate at the extremity, though it is 
seldom that one finds them in this perfect condition. It is possible 
that some of the rootlets did not bifurcate, but remained simple. 
Specimens of Stigmaria showing structure are not uncommon. 
The rhizome consists of a large pith surrounded by a zone of exo- 
genously developed scalariform tracheides, which is divided into a 
number of wedges by the thick primary medullary rays. These 
wedges again contain many less prominent secondary medullary rays. 
The vascular system is enclosed in a thick cortex. The cast of the 
pith cavity shows the impression of the netted cylinder of the vascular 
axis (Plate LIL, fig. 3), which is a distinguishing character between 
Stigmaria and Stigmariopsis. 
Stigmaria is the most common fossil one meets with in Carbon- 
iferous rocks. It is the rhizome of Lepidodendron, many Sigillarioe, 
and most probably also of Lepidophloios, though it has not been 
actually found united to the stems of the last-mentioned genus. 
Several species and varieties occur, the characters being founded 
on the size of the rootlet scars and the ornamentation of the outer 
surface of the bark. 
Stigmariopsis Grand 'Eury. Though this genus is closely 
related to Stigmaria, from the investigations of Solms-Laubach, it 
must, I think, be separated from it. It is true that little is known 
of the organisation of Stigmariopsis, but the little known appears 
sufficient to raise the fossil to generic rank. 
Stigmariopsis {Stigmariopsis anglica Kidston, Plate LL, fig. 4) 
is founded on Stigmaria-like rhizomes which are proportionately 
shorter and thicker. They spring from the hollow cup-like base of 
a Sigillarian stem in four primary arms, which again bifurcate, 
possibly several times. From the lower surface of the four primary 
divisions, immediately at the base of the trunk, spring downward 
directed conical growths — the tap-roots of R. Brown. The surface 
of the rhizomes and tap-root-like growths bear quincuncially-arranged 
rootlet scars, similar in structure to those of Stigmaria. Like Stig- 
