Physiologie. — Palaeontologie. 
55 
Wirkung ausüben, bei den Samen von Phacelia tanacetifolia Benth 
eine auffallende Förderung der Keimung durch die blauen Strahlen 
festgestellt wurde. Für die genannten Samen hat Remer eine kei¬ 
mungshemmende Wirkung des Lichtes, eine fördernde der Dunkel¬ 
heit nachgewiesen. Autorreferat. 
Arber, E. A. N. and H. H. Thomas, On the Structure of 
Sigillaria scuiellata, Brongn., and other Eusigillarian Sterns, 
in Comparison with those of other Palaeozoic Lycopods. 
(Phil. Trans. Roy. Soc. Ser. B. Vol. CC. p. 133—166. with 3 plates 
and 1 text-figure. 1908. Abstract in Proc. Roy. Soc. B. Vol. LXXX. 
p. 148-150, 1908.) 
This paper contains the first full account of the structure of the 
Eusigillariae or ribbed Sigillarias of the Rhytidolepis section. The 
material consisted of a petrifaction from the Lower Coal Measures 
of Shore-Littleborough in Lancashire, containing two well- 
preserved stems, tying side by side. The external surfaces ol the 
ribs of both stems have been exposed and the characters of the 
ribs agree with those of the impressions known as Sigillaria scutel- 
lata Brongn. 
The stele has a well-marked pith, a tissue which is not, however, 
preserved in any of the stems examined. The medullary cavity is 
bounded by a continuous ring of scalariform tracheides, — the pri- 
mary wood, — the outer margin of which is crenulated. The pro- 
toxylem elements lie at the apices of the blunt, rounded teeth of 
the corona. The elements of the protoxylem and primary wood 
appear to consist entirely of scalariform tracheides. The elements 
of the secondary wood are also scalariform, and are arranged radi- 
ally. The outer margin of this zone was crenulated, the ridges and 
grooves corresponding in position to those of the primary wood. 
The phloem and inner cortex of thin-walled elements are not 
preserved. A well developed band of phelloderm is found near the 
surface of the ribs. This is regarded as having arisen on the inner 
side of a meristematic zone. No definite cambiai layer is to be fuund, 
and it is suggested that the meristematic activety here took place 
periodically. The secondary tissue consists of prismatic fibres, often 
chambered. 
The ribs are really formed of cortical tissues, and not by 
fused leaf-bases. They consist largely of phelloderm, and exter- 
nally what is probably a small zone of primary cortex, which lay 
without the region of secondary meristematic activity, still persists. 
The stems were probably ribbed long before the formation of the 
periderm. The leaf-bases, consisting of thin-walled parenchymatous 
elements, merely form bracket-like projections from the ribs; those 
of the same vertical series being sufficiently distant from each other 
to leave a small gap of primary cortex between them. The ribbing 
of the stem in the Eusigillariae, being entirely independent of the 
form and arrangement of the leaf-bases, appears to be a natural 
feature of importance in classifying the Sigillariae. The presence ol 
a ligule and a ligular pit has been detected for the first time in 
petrified material. 
The course of the leaf-traces in the leaf-bases and cortical tissues 
has been followed. The bündle is collateral, and without secondary 
wood. In the leaf-bases the trace consists of a double xylem 
Strand, the two xylem groups being widely separated. These two 
