NOTE. 
A NOTE ON THE STRUCTURE OF THE CORTEX OF SIGILLARIA 
MAMILLARIS, Brongn. In a paper 1 on the structure of Sigillaria scutellata , , 
Brongn., published last year, we drew attention to some new points of interest 
in regard to the ribs, leaf-bases, and also the leaf-traces of the stem of this species. 
We have since had an opportunity of examining the anatomy of an excellent specimen 
of Sigillaria mamillaris , Brongn., recently acquired by the British Museum (Nat. 
Hist.) 2 . The material was obtained originally by Mr. Lomax from Shore-Little- 
borough, Lancashire. Mr. Lomax was able to expose the external surface, which, in 
the case of one rib, proved to be extremely well preserved. Thus, as with our 
specimens of Sigillaria scutellata , there has been no difficulty in determining the 
species by its external characters. 
The structure of the stele of another example, referable to the same species, has 
been already described by Dr. Kidston, 3 in a preliminary note published some two 
years ago. No reference, however, was there made to the anatomy of the cortical 
tissues, or of the leaf-bases. 
We do not propose to attempt a full account of the anatomy of the British 
Museum specimen, but rather to compare its structure on certain points with that of 
Sigillaria scutellata , especially in regard to the ribs and leaf-bases. 
Sigillaria mamillaris , like < 5 \ scutellata , is an Eusigillarian stem of the Rhytido- 
lepis type ; that is to say the stems are ribbed, and the ribs are separated by straight 
furrows. While, however, in S. scutellata the bracket-shaped leaf-bases are long and 
distant from one another, in S. mamillaris they are shorter (about 13 mm. in length) 
and closely approximated. In the former species, the successive leaf-bases of the 
same rib are separated by small areas of primary cortex. In the latter, the leaf-bases 
are merely marked off, above and below, by small transverse grooves, partly filled by 
a growth of cork. These grooves are more or less oval in form at the surface, and 
are not as broad as the rib. Their breadth decreases as we pass inwards from the 
surface, and more internally they assume a triangular shape. 
Thus the ribs of S. mamillaris are interesting as affording a transition stage 
between a Sagillaria with distant leaf-bases, such as S . scutellata , and a Favularian 
type such as S. tessellata , where the leaf-bases are very short but much broader, 
though equally approximate. The zigzag course of the grooves between the ribs in 
Favularian species appears to be due to the fact that the leaf-bases are more hexagonal 
1 Arber and Thomas: Phil. Trans. Roy. Soc., Ser. B, vol. cc, p. 133, 1908; Proc. Roy. Soc., 
Lond., B, vol. lxxx, p. 148, 1908. 
3 Nos. V. 11,403-11,418 in the General Collection of Sections in the Geological Department. 
3 Kidston : Proc. Roy. Soc., Edinburgh, vol. xxvii, p. 203, 1907. 
(Annals of Botany, Vol. XXX 1 L No. XCI. July, 1909] 
