Sykes. — The Anatomy and Morphology of Tmesipteris. 73 
on a branch with one leaf on each side, but here a synangium was formed 
at the termination of the main axis, there being one leaf on one side, but 
a second normal fertile branch in the corresponding position on the other side. 
A minute investigation of the structure of the stem near the apex 
(Fig. 4, a , b, c, PI. VII) shows that the cortex is here composed of only five 
or six layers of cells, the innermost of which does not in this region form 
the brown substance. The phloem often contains fibres, and is already 
lignified. The xylem forms a solid mass of scalariform elements with one 
group of protoxylem, which is also scalariform even to the last terminal 
element. In plants preserved while still growing in length a single apical 
cell can be made out with some difficulty. 1 
(f) Leaves. The leaves of the two forms are similar in structure, the 
chief difference consisting in the shape of their cross-section. In both 
species the little scale-leaves remind the observer of Psilotum. The lowest 
of these consist simply of a small mass of mesophyll, enclosed in a layer of 
epidermis. Mesophyll, epidermis, and stomata are of the characteristic 
nature described below for normal leaves. 
The ordinary leaf of T. elongata has stomata on both sides, but 
that of T. tannensis has stomata only on the adaxial side. The stomata 
are of the ordinary type, with two guard-cells and no accessory cells. 
Their development in the young leaf is of no especial interest ; they arise 
from an epidermal cell in the simplest manner by division into two. 
The epidermal cells of the adult leaf are large and stellate; their walls 
are thickened in bands (Fig. 6, PI. VIII), and when stained with Iodine Green 
and Eosin the bands stain green, while the areas in between them become 
pink. The mesophyll is composed of curious lobed cells (Fig. 5, PI. VIII), 
quite similar to those of Psilotum . 2 A single vascular bundle runs in an 
almost vertical direction through the cortex of the stem, traverses the centre 
of the leaf, and terminates in a single tracheide just below the mucronate tip. 
The bundle during the greater part of its course consists of four or five 
scalariform tracheides surrounding one or two narrowly scalariform 
protoxylem elements, and enclosed by lignified phloem and a more or less 
evident layer, which probably represents the endodermis. 
The base of the leaf is decurrent, and thus a cross-section of the leaf- 
bearing part of the stem shows one or more protuberances due to leaf 
bases, in which the lobed mesophyll is always conspicuous. 
(g) Fertile branches. In this description I can only include the fertile 
branches, but the resemblance between my sections of these and Bertrand’s 
figures of sections through a sterile branch 3 is most striking, and there seems 
some doubt whether sterile branches with no synangial rudiment are ever 
found. 4 
1 See Jennings and Hall, 1891, Pl. IV, Figs. 27, 28 ; PI. Ill, Fig. 18. 
* Ford, 1904. 3 Bertrand, 1 . c., Figs. 243-246. i Thomas, 1902. 
