497 
Mitrospermum compressum (Will.). 
as that suggested by Scott and Maslen 1 to explain the disappearance 
of the inner flesh in Trigonocarpus , namely, ‘ that the cells themselves were 
of a delicate nature, and also that the hard impermeable coat of the seed 
prevented the infiltration of the petrifying material before the tissue had 
undergone disorganization \ 
The inner flesh seems to correspond to the ‘ plaques tylaires ’ described 
by Bertrand 2 as characteristic of the species of Cardiocarpus found in the 
French Carboniferous rocks. 
D. The Vascular Supply. 
A vascular bundle (v.b. in Text-Fig. i) enters the hilum, and passes 
straight up to the base of the nucellus, through the foramen in the shell to 
which we have already referred. Below the nucellus, the end of the bundle 
expands, and gives off two opposite branches lying in the principal plane of 
the seed. These strands are at first almost horizontal, but they soon bend 
downwards and outwards, traversing the shell in an oblique direction 
(PL XXXVII, Fig. 9, and PI. XXXIX,Fig. 26). On emerging into the sarco- 
testa they curve upwards, and pass towards the micropyle, following the 
slight groove at the junction of the valves. We may infer that the bundles 
continued through almost the whole length of the seed, since they can 
be followed in transverse and longitudinal sections as far as the base of the 
micropyle, and tracheides have even in one case 3 been recognized close to 
the upper part of the micropylar canal. 
A small number of tracheides are given off from the expanded end of 
the central bundle, not far above its two main branches, mostly in the plane 
at right angles to the plane of flattening. Median sections, cut in the 
secondary plane, expose these tracheides running longitudinally to right and 
left at the base of the nucellus, and forming a thin, horizontal, tracheal plate. 
I have not been able definitely to satisfy myself as to whether a nucellar 
vascular system arises from this tracheal plate. The nucellus as a rule sur¬ 
vives only as a carbonized layer showing but little structure, though in 
certain of the sections in which it is better preserved, 4 elongated elements 
with indications of tracheal markings can be detected at various levels. It 
is possible that these elements may prove to be vascular. 
E. The Nucellus and Embryo-Sac. 
The nucellus seems to have been free from the integument from its 
base upwards, as in Stephanospermum 5 and Trigonocarpus . G The possi¬ 
bility that an appearance of freedom might be due to a contraction and 
tearing of the nucellar tissues must not be overlooked. There seems, how- 
1 Scott and Maslen (’ 07 ), p. no. 2 Bertrand (’ 08 *). 
3 U. C. L., S. 70. Cf. also D. H. S. 2254 and U. C. L., S. 35. 
4 e.g. U. C. L., S. 36, S> 53, S. 68, S. 69. 
5 Oliver (’ 04 ). e Scott and Maslen (* 07 ). 
