Sykes . — The Anatomy and Morphology of Tmesipteris. 75 
the decurrent bases of the two leaves ; stomata are present on both sides 
of the ridges, and are occasionally found on other parts of the axis. In 
between the two less projecting corners the synangium pedicel arises, and 
one of the three vascular bundles passes into this structure, while the 
other two are each continued into one of the two leaves. The structure 
of the leaves corresponds in every respect with that of the leaves of the 
main axis. 
The synangium itself is composed of two lobes, each containing 
spores, 1 and separated from each other by a plate of sterile tissue. The 
outer wall of the synangium consists of a single layer of cells with thickened 
walls. Dehiscence takes place along a double line of thin-walled cells, 
which traverses each lobe in a longitudinal direction (see Text-fig. IX, p. 74). 
Under the thick epidermal layer are two or three layers of ordinary thin- 
walled pitted parenchyma, which enclose the cavities containing the spores. 
Each of the pits is sometimes surrounded by a lignified ring. There is 
no definite tapetum ; the spores are formed in tetrads and are bilateral 
and oval in shape, resembling closely those of Psilotum. 
The pedicel of the synangium is very short, and is continuous with 
the plate of sterile tissue which separates the two lobes. Its vascular 
bundle terminates in this plate, and may end just on the edge of it 
(Fig. 8, PL VIII), or may run for a short distance across it (Text-fig. VIII, F, 
p. 74). In either case it gives off, just as it enters the synangium, a branch 
on either side, which run in opposite directions round the periphery of the 
plate, and sometimes meet on the other side, thus forming & complete 
ring. All the xylem of the synangial trace is contained in this ring, and 
the cells of the plate are also found to be lignified to a considerable 
extent. The phloem constituent of the synangial vascular supply is much 
greater in bulk than the xylem, and extends for a short distance up the 
walls of the spore cavities (Text-fig. VIII, H, p. 74). It is composed of 
rather short sieve-tubes with lignified walls. A series of tangential sections 
through the synangium shows clearly (1) the single bundle in the pedicel 
(Fig. 9, PI. VIII) ; (2) the division of this bundle into three (Fig. 10, PL VIII) ; 
(3) the disappearance of the central trace and wide separation of the two 
lateral ones on either side of the sterile plate (Fig. 11, PL VIII) ; (4) and 
finally at the side of the synangium furthest from the axis these also die 
out, or are represented by a small amount of phloem only. 
(h) Abnormal branches. The material supplied to me contained very 
few abnormalities in comparison with those described by Thomas 2 . 
i. One of the plants bore a three-sporangiate synangium near the apex. 
The main axis gave rise first to a branch bearing this synangium and two 
leaves, then to a single leaf, and was finally terminated by an ordinary 
1 For development of spores see Jennings and Hall, 1891, PI. V, Figs. 40-42. 
2 Thomas, 1902. 
