THE PALJEOZOIC SEED LAGENOSTOMA OVOIDES. 415 
Right at the apex, the cusps of the canopy lining fit into the external 
ridges, the inner and outer epidermis nearly, if not quite, meeting at these 
points (РІ. 28. fig. 14 and PI. 24. fiy. 34). Тһе soft tissue has thus quite 
disappeared, and it is therefore clear that the micropylar grooves are not due 
to “ contraction or collapse of the filling tissues of the chambers,” as it has 
been thought possible for L. Lomawit (16, p. 105), nor to any superficial 
modification which petrifieation might possibly induce, but are a perfectly 
definite feature in the structure of the seed. It does not seem to me likely 
that the apical grooves and ridges are even exaggerated, far less produced by 
post-mortem changes. 
% The Nucellus. 
A description of the nucellus resolves itself into that of the lagenostome 
and plinth, since in no preparation is there any further trace of the mega- 
sporangium, with the exception of the thick, structureless, nucellar membrane. 
Although described as confluent with the integument as far as the plinth, 
which it undoubtedly was in life, this membrane is frequently seen to be 
torn away from the soft tissue—more often than not dragging the bundles 
with it. As it is usually crumpled, parts of the membrane are sometimes 
caught in surface view, when a pitted appearance is generally presented ; 
but it is doubtful if this is other than an effect of the impregnating mineral. 
Indeed, the entire nature of the nucellar membrane is a matter of un- 
certainty : i. e., was it originally a thick membrane, or does it represent a 
broken-down tapetal layer ? 
The lagenostome is about 1 millimetre long, and ‘8 mm. in its greatest 
breadth. The central cone is mainly composed of thin-walled, roughly 
spherical cells, about 40 и in diameter, between which intercellular spaces 
occur. А good transverse section across the body of the lagenostome shows 
a central group of six or eight cells (Pl. 83. fig. 16), which are much smaller, 
being only about 20 or 30 ш in diameter ; and a few longitudinal sections 
reveal that these cells reached a length of at least 100 u, and together formed 
a median column, extending from the base to a distance varying from one to 
two thirds the height of the lagenostome. The whole of the apex of the 
central eone is modified by having the cell-walls strongly thickened to a 
varying distance in a downward direction, with the result that a dark 
tongue-shaped mass was formed, the central cells of which were elongated 
atleast in the lower part. None of the cells of the central cone seem to 
show contents. 
As before stated, the central cone is detached from the outermost layer 
of cells or wall of the lagenostome to form a space which is the actual 
pollen-chamber. It is not, however, perfectly clear that this space was 
always continuous around the organ in its whole extent. Many sections 
