204 Proceedings of the Royal Society of Edinburgh. [Sess. 
most. These are succeeded inwards by large tracheids, which have a tendency 
to arrange themselves in irregular rows (fig. 1). 
The secondary xylem consists of regular rows of tracheids of smaller 
size than those of the primary xylem, but they increase in size from within 
outwards, though they never attain to the dimensions of those of the 
primary wood. Passing out through the secondary xylem are the 
medullary rays. 
If the structure of the primary wood of Sigillaria mamillaris be com- 
pared with that of Sigillaria elegans, their great similarity is very striking. 
The only point in the primary xylem by which the two species could be 
separated is the protoxylem groups, which in Sigillaria mamillaris contain 
a 
Fig. 1 . — Sigillaria mamillaris, Brongt. Portion of primary xylem. a, protoxylem groups, x 30. 
fewer elements and do not form such prominent projections as in Sigillaria 
elegans. Notwithstanding this great similarity of internal organisation in 
these two plants, the external form and arrangement of the leaf scars 
precludes the possibility of regarding them as having close specific 
relationship. 
In the other example which I refer to Sigillaria mamillaris , but of 
which the outer surface was not seen, the matrix surrounding the specimen 
shows several transverse sections of Sigillarian leaves, some of which show 
a single vascular strand, whilst others mixed with them show the double 
strand, and are, in fact, the Sigillariopsis of Renault * ; but it will be seen 
* Renault, “Structure comparee de quelques tiges de la flore carbonifkre,” Nouv. 
Archives dn Museum , vol. ii., 2 e ser., p. 270. PI. xii. figs. 15-19 (, Sigillariopsis Decaisnei ) ; 
PI. xiii. figs. 1-4 ( Sigillariopsis , sp.), 1879. See also Renault, Bassin houil. et perm. d’Autun 
et tfEpinac, Flore foss., fasc. iv., deux, part, 1896, p. 245 ; Roche, “ Biographie de Bernard 
Renault, avec extrait de ses notices scientifiques,” Mem. Soc. dhist. nat. d'Autun, vol. xviii., 
1905, PI. ii. figs. 11-15. 
