[22 Scott and Masleit . — The Structure of Trigonocarpus . 
it probably would be if the nucellus were free only at the tip as in the 
Cycads, we believe that in Trigonocarpus the nucellus was free from the 
integument throughout its whole length. 
The Pollen- Chamber. — Above the prothallial region of the nucellus is 
seen a relatively small pollen-chamber (PL XII. Fig. 13, p.c.), a very 
characteristic feature in these old seeds. This structure in Trigonocarpus 
was indicated in some of the figures of Hooker and Binney x , and after- 
wards described and more fully illustrated by Williamson 2 . Curiously 
enough, the best preservation of the pollen-chamber which we have yet seen 
is in one of the original Hooker and Binney slides, now preserved in the 
Binney Collection at Cambridge, and figured in our PI. XII, Figs. 13 and 14, 
and PI. XIV, Fig. 32. 
As shown in PI. XII, Fig. 13, the pollen-chamber forms a wide dome, 
2-5-3 mm - in diameter at the base. We have to add the new fact that the 
pollen-chamber was provided at the top with a narrow channel or beak, be , 
not more than 300 /u in diameter. The presence of a beak is also obscurely 
indicated in the Williamson section (1478 w.), which is shown in Fig. 114 
of his Memoir before referred to. The beak, as shown in the Binney slide, 
is barely half a millimetre in length, but presumably it extended much farther 
in the natural condition, and connected the pollen-chamber with the micro- 
pyle, or even extended for some distance along the latter. 
The pollen-chamber as a whole is smaller than in Stephanospermum. 
In X. caryoides the pollen-chamber forms about one-seventh of the height 
of the whole nucellus, and in X. akenioides about one-fourth or one-fifth 3 , 
while in Trigonocarpus Parkinsoni the proportion, judging from the Binney 
section represented in PI. XII, Fig. 13, and excluding the beak, is about 
one-tenth. In general structure the pollen- chamber of Trigonocarpus 
appears to have been very similar to that of Stephanospermum , but on 
account of the small number of sections in which the pollen-chamber is 
shown and the imperfect preservation, it is impossible to describe its struc- 
ture in much detail. The megaspore wall was doubtless separated from 
the cavity of the pollen-chamber by a transverse septum continuous with 
the nucellus. In PL XII, Fig. 13, the septum is wholly destroyed, unless 
the pad of tissue shown at p. has been displaced from the floor of the pollen- 
chamber, as is probably the case. In other sections 4 (not figured) part 
of the septum remains at the sides. 
In Stephanospermum akenioides the septum between the megaspore 
and the pollen-chamber is a vascular sheath consisting largely of tracheides 
continuous with those of the wall of the nucellus below and around, thus 
completing the vascular investment of the nucellus 5 . Tracheides are never 
1 Hooker and Binney (’55), PL IV, Figs. 7, 8, 12. 
2 Williamson (’77), PI. XIII and XIV, Figs. 1 13-15. 
3 Oliver (’04) (1), pp. 363, 374. 4 e. g. 940 (S) \ Wild 1939 (S). 
5 Oliver (’04) (1), p. 369. 
