Oliver. — 'The Ovules of the older Gymnosperms. 453 
able genus of Taxaceae, which though siphonogamous yet 
appears to retain marked traces of those contrivances which 
usually became obsolete when siphonogamy appeared. Finally 
we can hardly close this article without some allusion to such 
elementary seed-like structures as have been described, with 
a view to linking up the Seed Plants with the true Pteri- 
dophytes. But in this department, though facts that will be 
of the greatest value hereafter have already come to light, 
some time must elapse before we are able to realize step by 
step the manner of origination of the earliest seeds. 
1. Ordinary Palaeozoic Seed Types. 
These in their simplest form are represented by Stephano - 
spermum 1 , a small unassigned seed some 10 mm. in length, 
5 mm. in diameter, and circular in transverse section. This 
seed may be taken as the type of a group of radially sym- 
metrical seeds— many with ridges and other excrescences 
often fantastic in character. For convenience all such forms 
were ranged together provisionally by Brongniart, and for the 
sake of easy reference may be termed the Radiospermeae 
(= Brongniart ’s Group B) 2 , in contradistinction to the flattened 
seeds or Platyspermeae ( = Brongniart’s Group A) of which 
a few are known to belong to the Cordaiteae. 
The members of these two provisional groups differ in 
other respects than in their form. Whilst the Radiospermeae, 
with rare exceptions 3 , possessed a bony integument only, the 
Platyspermeae were in all cases provided with an additional 
external fleshy layer, the sarcotesta. And there were further 
differences in the internal organization of these two groups, 
though they are not of such a character as to upset the broad 
general resemblance that embraces all these seeds. In the 
briefest possible manner a type from each group may now be 
1 Cf. Brongniart, Les graines fossiles silicifiees, PL XVI. 
2 Brongniart, loc. cit., p. 20. 
3 Trigonocarpus pusillus , Brongniart, and Tripterospermum , in the sense of 
Brongniart. Cf. loc. cit., p. 26, footnote. These had a sarcotesta in addition to 
a bony scelerotesta. 
I 1 3 
