Affinities of the Palaeozoic Seeds of the Conostoma Group . 41 
In this connexion it is interesting to note that in Stangeria and Ginkgo , 
as figured respectively by Lang 1 and Hirase , 2 the apical papilla of the 
nucellus which becomes perforated is limited by a prominent epidermis, as 
to which Lang remarks, 4 The superficial cells of the pointed tip seen in 
Fig. 1 2 have their walls thickened and form a very definite boundary to the 
sides of the chamber, suggesting a close comparison with the corresponding 
region of certain fossil gymnospermous seeds .’ 3 The actual place which 
the pollen reached — the ‘ pollen-chamber ’ — is found at a deeper level, 
a statement also holding good of the fossil seeds to which passing reference 
has been made. Thus, whilst the facts in so far as they are known are 
consistent with an elaboration of the nucellus, on lines analogous to Cono- 
stoma, in the seeds of the Medulloseae, Cordaiteae, recent Cycads, and 
Ginkgo , to say that the beak of the nucellus in these seeds corresponds 
with a vestigial lagenostome, and the pollen-chamber with a plinth cavity, 
would be premature if not erroneous. Much fuller details of ovular develop- 
ment than are yet available are required before we can advance further. 
Before leaving this part of the subject reference may be made to the 
presence in several siphonogamous Gymnosperms of examples of ovules of 
which the nucellus undergoes spontaneous disintegration at the apex before 
the arrival of the pollen. Whilst this procedure would appear to be the rule 
in the three genera of Gnetales, in Ephedra 4 and Gnetum 5 it was carried so 
far that definite excavations or ‘ pollen-chambers ’ were produced. The func- 
tional significance of this peculiarity in plants whose fertilization is accom- 
plished by the agency of pollen-tubes is far from evident, and we must 
await new light from current or future investigations. We would only re- 
mark in this connexion that the past history of the Gnetales and of such 
Conifers as show analogous arrangements 6 may be the determining factor in 
the possession of a mechanism which has somewhat the appearance of being 
an anachronism. 
VII. General Discussion on the Testa. 
The ribbing, which is so general a character of these and allied seeds, 
is broadly an indication of a multiple origin of their integuments. What- 
ever the nature of the members which coalesced to form this organ, it seems 
reasonable to assume that primitively each of the coalescing members had 
its own vascular strand, and that the correspondence which usually obtains, 
both in number and in position, between the ribs and bundles, is an 
expression of one and the same fact, viz. the multiple origin. In Physostoma 
1 W. H. Lang : Ann. of Bot., vol. xiv, PI. XVII, Fig. 15. 
2 S. Hirase : Journ. Coll. Sci. Tokyo, vol. xii, PL IX, Figs. 31 and 32. 
8 Lang: loc. eifc., p. 286. 
4 W. J. G. Land : Bot. Gaz., vol. xxxviii, PL V, Fig. 44. 
5 Lotsy : Ann. Jard. Bot. Buitenzorg, vol. xvi, PL V, Fig. 35. 
6 e. g. Sciadopitys verticillata ; see Lawson, Ann. of Bot., vol. xxiv, PI. XXIX, Fig. 13. 
