Affinities of the Palaeozoic Seeds of the Conostoma Group. 19 
and R. 11 6 (PI. II, Fig. 18, and PI. I, Fig. 6). The plug which formed the 
floor is only slightly displaced in R. 116 (Fig. 6, Is.), whilst in R. no (PI. II, 
Fig. 14, Is.) the cushion of soft tissue which hangs suspended from the lower 
rim of the lagenostome appears to be still in position. 
The central cone of soft tissue that projected into the cavity of the 
pollen-chamber of Lagenostoma Lomaxii (Text-fig. 12, p. 39) does not 
appear to be represented in any of our specimens of Conostoma , though 
from analogy with that seed we regard it as certain to have been present 
in early developmental stages. Its absence from our specimens is best to be 
explained as a consequence either of very early deliquescence in develop- 
ment or imperfect preservation. 
Before turning to the plinth cavity and its contents it will be convenient 
to mention a general character of this organ. 
In occasional specimens of Conostoma we find that the plinth had not 
reached its full height, and as a rule lack of extension in this region seems 
to be correlated with other features which support the view that such 
specimens belonged to a younger stage of development than that usually 
found. Thus, in R. 114 (Fig. 2), where, having regard to plane of section, 
the plinth is only half the usual height, the testa is immature and shows 
progressive sclerization. Again, in R. 122 (Fig. 3), a very immature 
specimen as judged by the testa, no trace of the plinth is visible, though 
were the specimen a normal one this region should fall within the plane of 
section. In view of these data and of the well-ascertained fact that the 
plinth is undeveloped in the small-sized seeds of Lagenostoma Lomaxii l 
there is good reason for supposing the plinth to have arisen as an inter- 
calation at a relatively late stage in development. This extension of the 
nucellus just below the lagenostome must of course have been accompanied 
by a corresponding elongation of the free part of the testa, for, as we 
have seen, the relations between plinth and integumental lining were of 
the closest. 
The cavity of the plinth now claims attention. It was a hemispherical 
chamber of variable height, as we have seen, extending from the tapetal 
septum, which formed its floor, up to the lagenostome. Its maximum 
height all over was 0-5 mm. ; centre of floor to base of lagenostome, 
0-3 mm. Its contents, which only partly filled it, included (1) remnants of 
the soft interior tissues of the plinth, (2) pollen-grains. So far as information 
is afforded by our preparations, pollen when present in the seed was invari- 
ably contained in the plinth cavity, not in the lagenostome. 
The soft interior tissue of the plinth is mainly preserved in the form of 
a horizontal, circular cushion which in section has the form of a concavo- 
convex lens, the convex side being uppermost. This cushion or lens, which 
1 Oliver and Scott: On Lagenostoma Lomaxii. Phil. Trans., B, vol. cxcvii, p. 212, PI. IV, 
Figs. 1 and 2. 
