A ffinities of the Palaeozoic Seeds of the Conostoma Group. 1 7 
a mere shell — usually completely carbonized and appearing as a continuous 
black, structureless crust (cf. specimen R. 123, PL II, Fig. 19). Occasionally, 
the individual cells of which this shell was composed are preserved (speci- 
men R. 1 14, PI. I, Fig. 2,//.), showing it to have consisted of a single layer 
of flattened epidermal cells destitute of special sculpturing. 
Tracing this layer down the steep slope of the plinth to the level at 
which the tissues of nucellus and integument became confluent (R. no, PI. II, 
Fig. 14), it is found to curve sharply outwards and upwards (below j.), re- 
turning on its course as the lining layer of the integument which fitted the 
plinth like a jacket (cf. p. 14). 
Followed in the other direction the epidermis of the plinth dips 
slightly at the summit to form the depression in which the lagenostome was 
lodged. It does not, however, reach the 
central part of this recess, which, as 
sections across this region clearly prove, 
was perforated (specimen R. 117, PI. II, 
Fig. 16). The epidermis of the plinth 
at the insertion of the lagenostome 
curves abruptly upwards and outwards, 
and at the same time, changing com- 
pletely its histological character, becomes 
evaginated to form the sculptured wall 
of the lagenostome (PI. II, Fig. 18). 
Thus we see that the epidermal layer 
of the interior of the seed is in complete 
continuity throughout and that the 
various regions termed the micropylar 
tube, micropylar funnel, plinth jacket, plinth and lagenostome walls, are 
merely different specialized portions of one and the same layer. 
The lagenostome was a tiny goblet-shaped body, the cavity of which 
communicated with the plinth cavity. In shape it was slightly pyriform, 
its greatest horizontal diameter being about one-third up from its insertion. 
The mouth, which is rarely if ever shown in the sections, communicated 
directly with the micropylar tube, with which it closely engaged by 
a bevelled flange from the latter (Text-fig. 5, and PI. II, Fig. 18). Unlike 
Physostoma and Lagenostoma , the mouth was unprovided with any tube or 
beak. In the former the mouth was placed on a low papilla (Text-fig. 12, 
p. 39), whilst in the latter the tapering tube of the pollen-chamber reached 
the surface of the seed (Text-fig. 12). 
The principal dimensions of the lagenostome of Conostoma oblongnm 
were as follows — greatest horizontal diameter, 0-23 mm. ; diameter at 
mouth, o-i2 mm. ; height, 0-15 mm. 
In Physostoma the lagenostome or pollen-chamber was 1 mm. high 
c 
Text-fig. 5. Conostoma oblongum. 
Diagram of median vertical section of 
lagenostome to show how it was enclosed 
by the micropylar tube and funnel, m.t ., 
micropylar tube ; m.f , micropylar funnel ; 
p.l., wall of plinth; M.f. and tf, upper 
and lower flanges holding lagenostome (/) 
in place. 
