Scott and Mas ten . — The Struchtre of Trigonocarpns . 123 
found beyond the septum, i. e. they never penetrate to the walls or roof of 
the pollen-chamber itself. In our specimens of Trigonocarpns no trace can 
be seen of tracheal elements either in the septum or in the walls of the 
pollen-chamber, excepting, perhaps, in the beak to be described later. In 
the case of the septum this negative evidence does not necessarily imply 
that tracheides were absent, as the septum in our specimens of Trigono - 
carptis is only poorly preserved, but the absence of tracheides in the pollen- 
chamber wall in such a slide as that shown in PI. XII, Fig. 13, when quite 
well-preserved tracheides are seen lower down in the nucellus in the same 
section, appears to indicate that such elements were probably really absent. 
In this respect, then, Trigonocarpns probably agrees with Stephanospermum. 
In all the slides the megaspore membrane (PL XI, P"ig. 5, mi) is con- 
tracted away from the nucellus and from the septum above, but doubtless 
in the natural condition the two tissues were in close contact all round. At 
the apex, as suggested by Professor Oliver for Stephanospermum 1 , the 
megaspore membrane probably bulged the septum upwards, so that the 
septum and the top of the megaspore encroached somewhat on the pollen- 
chamber, and may have reduced its size considerably from that which 
is shown in PI. XII, Fig. 13, p.c. As in Stephanospermum , the pollen- 
chamber was provided laterally with cushions or shoulders of nucellar tissue 
of considerable thickness, composed of thin-walled elongated cells, the 
elongation being parallel to the slope of the wall. One of these cushions is 
shown in PI. XII, Fig. 13, c., and the other on the opposite side of the 
pollen-chamber is quite visible in the slide, although not in the photograph. 
The patch of tissue shown at p. in this figure is probably not a portion 
of one of the cushions, but, as shown by comparison with other slides, part 
of the floor of the pollen-chamber displaced from its natural position. The 
tissue of the cushion dies out on the roof of the pollen-chamber. 
The wall of the pollen-chamber is covered externally by a layer of 
epidermal cells apparently similar to, and doubtless continuous with, those 
of the nucellus below. When traced to the base of the nucellar beak 
the epidermal cells become radially elongated and palisade-like in form 
(PI. XII, Fig. 14, w). A somewhat similar change in the epidermal cells 
of the pollen-chamber wall has been described by Professor Oliver in 
Stephanospermum caryoides . In this form the flanks of the pollen-chamber 
are included in a well-marked epidermis of cubical cells which become 
columnar as the insertion of the beak is approached 2 . 
In Trigonocarpns P arkinsoni^ within the epidermal cells of the pollen- 
chamber beak, there is an inner layer of small prosenchymatous elements, 
shown in PI. XII, Fig. 14, t., and PI. XIV, Fig. 32, t. These fibrous 
elements are not more than about -oi mm. in width, and when examined 
under a high power and with good illumination exhibit a very faint * barring 5 
1 Oliver (’04) (i), p. 364. 2 Oliver (’04) (1), p. 374 and PI. 44, Fig. 38. 
