39 
The So-called Phloem of Lepidodendron. 
the plant, by a zone of secondary tissue consisting largely of serially 
arranged parenchymatous cells and including scattered groups of 
secondary tracheids. Beyond the primary xylem in a young stem or 
small twig, or external to the secondary xylem in an older or larger 
specimen, there is a cylinder of tissue internal to the cortex; this is 
limited by an endodermal layer, the position of which can be 
recognised in well preserved sections. It is the nature of this tissue, 
which consists of two well-marked zones, that I wish to discuss. 
In the other species, L. Wunschianum 1 , as represented by a magni¬ 
ficent specimen from the Lower Carboniferous rocks of Scotland, 
there is a central pith of parenchyma surrounded by a ring of 
primary wood, but in this type the secondry xylem which makes its 
appearance at a more advanced stage in the growth of the plant, 
consists entirely of rows of scalariform tracheids and medullary rays. 
Beyond the xylem there is a zone of tissue similar to that in 
L. fuliginosum, and in both species numerous leaf-traces occur in 
the extra-xylem region, passing upwards in an almost vertical course 
before they bend outwards into the cortex. 
Lepidodendron fuliginosum. The best specimens of this type 
that have come under my notice, as regards the preservation of the 
delicate tissues, are contained in the Binney collection, Cambridge. 
It is unnecessary to repeat the detailed description of these 
specimens, which I published in the Proceedings of the Cambridge 
Philosophical Society in 1899 2 , but the following passages may be 
quoted as dealing more particularly with those anatomical features 
for which Professor Weiss 3 has recently suggested a different 
interpretation. “ The xylem of the stem is surrounded by a fairly 
broad band of short and slightly flattened cells constituting a tissue 
to which the term meristematic zone has been applied; the reason 
for this appellation is that in some of the sections certain cells in 
this region are in a state of meristematic activity, and an identical 
band of short-celled parenchyma in the large Dalmeny stem was 
found to be the seat of active cell-formation. The formation of 
secondary tissues has scarcely begun in the sections with which we 
1 It is possible that this plant is identical with L. Harcourtii With. 
See Seward and Hill, 1900. “ On the structure and affinities 
of a Lepidodeudroid Stem, etc.” Trans. R. Soc. Edinburgh , 
vol. xxix, pt. iv., 1900, pp. 921 et seq. 
2 Seward, 1899. “Notes on the Binney Coll, of Coal-Measure 
Plants.” 
3 Weiss, 1901. “ On the Phloem of Lepidophloios and Lepidodendron.” 
Mem. Proc. Manchester Lit. & Phil Soc., vol. xiv, pt. iii., p. 1. 
