I 2 I 
Scott and Maslen . — The Structure of T rigonocarp u s. 
tracheides can be traced continuously for about a quarter of the circum- 
ference of the nucellus, so that there is no doubt as to their forming 
a continuous investment to the megaspore in this part of the seed. Higher 
up in the body of the seed the tracheides appear to range themselves in 
more or less definite longitudinal bundles, which are connected by transverse 
anastomoses running in a tangential direction. The structures observed 
are shown in PI. XIV, Figs. 30 and 31. Fig. 30 shows a portion of 
a transverse section of the nucellus, including one of the outwardly directed 
processes already mentioned. On the inner side of the nucellus a flattened 
longitudinal nucellar bundle is shown, n.b. The tracheides of which the 
strand is composed are usually much flattened radially, as shown in the 
figure. In its central part the bundle shown is about three elements thick, 
but laterally it becomes reduced to but one layer of longitudinally running 
tracheides. 
PI. XIV, Fig. 31, is drawn from the same transverse section as Fig. 30, 
and shows at the lower end part of one of the flattened longitudinal bundles, 
n.b., consisting of fairly thick-walled elements which can be seen to be 
tracheides in other parts of the section where the nucellus is cut somewhat 
obliquely. Outside the longitudinally running tracheides — cut transversely 
in the section — other tracheides, t., are shown running in a horizontal or 
oblique direction. Laterally, as shown in the upper part of Fig. 31, the 
longitudinal tracheides disappear, and are replaced by others which run in 
an approximately horizontal direction, and so form transverse anastomoses 
between the longitudinal bundles. Similar longitudinal strands are seen in 
this section opposite to other projections on the outer side of the nucellus. 
The nucellar tracheal system has been traced through the whole length 
of the nucellus, almost to the base of the pollen-chamber. There is no 
evidence of phloem in connexion with the nucellar tracheides. 
A tracheal investment of this kind to the megaspore appears to have 
been a common feature of many of the old Cycadean seeds of the Palaeozoic 
era. Prof. Oliver has described a somewhat similar tracheal investment in 
Stephanospermum. In Stephanospermum akenioides the structure of the 
nucellus as a whole is almost identical with that of Trigonocarpus P arkinsoni, 
excepting that, whereas in Stephanospermum the tracheal mantle forms a 
thin but continuous sheath without trace of local segregation into bundles 
in Trigonocarpus there are definite longitudinal bundles. 
The question of the relation of the nucellus to the integument, whether 
coherent with it throughout the greater part of its extent as in the modern 
Cycadeae, or free from it as in Stephanospermum or Lagenostoma , is one of 
importance. From the fact that the nucellar epidermis in Trigonocarpus 
can be traced throughout the whole length of the nucellus from the chalaza 
upwards, as in Stephanospermum , and is not confined to the upper part, as 
1 Oliver (’ 04 ) (1), pp. 367, 368. 
