98 Scott and Maslen . — The Structure of Trigonocarpus . 
The sclerotesta is in many cases the outermost tissue preserved, but in 
good specimens this is succeeded on the outside by a delicate, thinner- 
walled tissue, the sarcotesta (PL XI, Fig. 5, set). This layer is never 
preserved in its entirety, owing to its weak construction and to its position 
on the outside of the seed, though parts of it may be perfect. Owing to 
the more or less collapsed condition of the sarcotesta, it is impossible to 
make an accurate estimate of its total thickness in the natural state, but it 
must certainly have exceeded 2 mm., and was probably considerably 
thicker than this. The sarcotesta is bounded on the exterior by the well- 
differentiated limiting layers to which Mr. Wild first directed attention \ 
and traces of which are found in most of the best slides (see PI. XI, Figs. 
1, 3> 5> 6, 7, 8, /., PI. XII, Fig. 11, h. and e., and PI. XIV, Fig. 23). 
The two layers of the testa, when traced upwards, are continued into, 
and form the walls of, the long micropylar beak to which we have already 
drawn attention. 
The sclerotesta of the micropylar beak is, in its lower part, more or 
less triangular in transverse section (PI. XI, Fig. 7, /.), and throughout 
the greater part of its length the beak possesses a triangular central tube 
or micropylar canal. Outside the sclerotesta of the beak is a great 
development of the sarcotesta, appearing, as seen in the transverse sections, 
as a wide flat wing on either side of the micropyle (see PI. XI, Figs. 7, 8, 
and PL XII, Figs. 9, 10). The ‘ wing ’ is bounded externally by the 
usual limiting layers. The question as to how far the flattened, wing-like 
form is natural, and how far it is caused by loss of the internal tissue of the 
sarcotesta and flattening by pressure is difficult to answer, but will be 
discussed later in this paper. Within the testa of the body of the seed, 
and usually separated from it by a space, is the nucellus (PL XI, PTg. 5> n.). 
Longitudinal sections show the chalazal attachment of the nucellus at the 
base of the seed (PL XII, Fig. 12, /.). Above the chalazal attachment 
the nucellus appears to have been free from the integument, agreeing in 
this respect with Stephanospermum 2 and some other Palaeozoic seeds, and 
differing from the modern Cycads, in which only a comparatively small 
upper portion of the nucellus is free. This view of the relation of nucellus 
and integument has already been suggested by Professor F. W. Oliver for 
a French form, Trigonocarpus pusillus 3 . At the micropylar end of the 
nucellus is the pollen-chamber, long ago indicated in some of Hooker and 
Binney’s figures, and described and more fully illustrated by Williamson. 
The pollen-chamber (PL XII, Fig. 13, p. c .) forms a wide dome 2*5~3 mm. 
in diameter at the base, and was provided at the top with a narrow beak 
or canal, be. not more than 300 [i in diameter (see also PL XII, Fig. 14). 
In the section figured the pollen-chamber beak is barely half a millimetre 
in length, but presumably it extended much farther in the natural condition. 
1 Wild (’00). 2 Oliver (’04) (i), p. 368. 3 Oliver (’04) (2), p. 99. 
