492 Agnes Arber.—On the Structure of the Palaeozoic Seed 
a decade. In the case of the Platysperms less progress has been made. 
A number of these seeds, occurring in the silicified pebbles from the French 
Upper Palaeozoic rocks, were long ago described by Brongniart, 1 and 
subsequently figured. 2 Quite recently Bertrand 3 has revised Brongniart’s 
work, in the light of Renault’s preparations, and has amended the generic 
and specific diagnoses. Williamson, 4 working about the same time as 
Brongniart, contributed a description and figures of a flattened seed from 
the British Carboniferous rocks, which he named Cardiocarpon compression . 
His description was necessarily incomplete owing to the fact that he had 
very few specimens, and that his more important sections were not thin 
enough to reveal the detailed structure. Since Williamson’s paper was 
published, no further advance seems to have been made in our knowledge of 
the internal structure of British Platysperms. 
Seeds similar to those figured by Williamson under the name of 
CardiGcarpon compression occasionally occur in , sections of the English 
Lower Coal Measure nodules, or 4 coal-balls ’. Professor F. W. Oliver, who 
had formed a collection of such preparations, suggested to me that I should 
undertake their examination. I am also indebted to Dr. Scott and Professor 
Weiss, who had both been collecting sections of Cardiocarpon compression 
with a view to their ultimate description, and who very generously made 
over to me the whole of their material. Miss Benson and Mr. D. M. S. Watson 
have also been so good as to lend me sections which have been of great 
value. The following account is based mainly on the preparations in the 
University College Collection, supplemented by those from the sources 
above acknowledged, and from the Williamson Collection in the British 
Museum. I am indebted to Dr. Smith Woodward for permission to 
examine the latter. The present investigation, on which a preliminary 
note has already been published, 5 was begun at University College, London, 
and I wish to express my gratitude to Professor F. W. Oliver, under whose 
direction it was undertaken. I have also to thank Dr. Scott for his help 
and advice in connexion with the study. 
In the present paper I propose to use the new generic name Mitro - 
spermion in lieu of Cardiocarpon for the seed under discussion. The reasons 
for this change will be deferred until the structure has been considered. 6 
II. General Characters of the Seed. 
A. The Sclerotesta. 
The seed is a characteristic Platysperm. It is symmetrical about two 
planes. The first is the plane of flattening, or in other words the plane 
which traverses the longer axis of the transverse section (Text-Fig. 2, C,/./.). 
1 Brongniart (’74). 2 Brongniart (’81). 8 Bertrand (’07 and ’08). 
* Williamson (’77). 5 Agnes Arber (’10). 6 See p. 502 . 
