44 Salisbury . — On the Structure and Relationships of 
micropylar tube, the angles being continuations of the ribs lower down, into 
which they pass by a hollow curve. 
Within the sclerotic tissue was a fourth layer, probably confined to the 
micropylar region and representing the £ inner flesh ’ of related seeds. 
The megaspore cavity was much less pointed at the base than was the 
hard shell around, and through this divergence of the two surfaces a chalazal 
cushion of sclerotic tissue was formed from which arose a nucellus, that stood 
up erect and free within the seed cavity, surmounted at its apex by a large 
pollen-chamber. 
The nucellus was bounded at the exterior by a well-differentiated 
epidermis, and within was a tracheal sheath forming the upward continua- 
tion of a single vascular strand which pierced the chalazal cushion. 
The vascular organisation was essentially similar to that of other seeds 
of this group, and consisted of a sarcotestal system of bundles without and 
a nucellar system within. 
Neither pollen nor prothallus are preserved in any of our sections, which 
may indicate that all our specimens were abortive ovules, though the 
presence of numerous fungal spores within the megaspore cavity may 
indicate its former occupation by an organized tissue which served as 
nourishment to the saprophytic organisms. 
III. The Testa, 
i. The Sclerotesta. 
The obovoid sclerotesta had an average thickness of about 0.5 mm. and 
bore, as we have seen, six longitudinal ribs, of which the three major persisted 
as far as the triangular beak. At the apex these ribs pass gradually into 
the three angles of the micropyle, and, except at the base, are commissured. 
The major ribs from the base of the micropyle to within some 6 mm. of the 
chalazal extremity have about the same radial extent, but exhibit varying 
development in the different specimens (0-75 mm. from surface in S. 33, a-e , 
to i*4 mm. in S. 31, a-k). The three minor ribs alternated with the three 
major, were without commissures, and attained their greatest extent (0-4 mm.) 
about 2 mm. from the base, above which point they gradually diminished and 
finally died out some 8 mm. from the chalaza. At the base of the seed 
the sclerotesta formed a solid inverted cone about 3*5 mm. high, perforated 
by a narrow canal through which the single vascular bundle passed to the 
floor of the nucellus. The base of this cone projected upwards as a dome- 
shaped papilla about 0-5 mm. high and 1-5 mm. in diameter, and its margin 
served as the place of attachment for the nucellar epidermis. As the ribs, 
both major and minor, approached the chalazal end they became gradually 
smaller till at the extremity all indication of ribbing had disappeared. The 
cavity within the sclerotesta was, owing to the sclerotic papilla, much blunter 
