306 GYMN-OSPEEMOTJS SEEDS [CH. 



with foliage of which we have not yet discovered any traces, 

 probably because these Gymnosperms did not flourish upon the 

 low swampy grounds which were the homes of the great mass 

 of the coal-producing plants^.' Prof. Zeiller^ has also drawn 

 attention to the numerical excess of seeds over vegetative organs. 

 This discrepancy has to a large extent been explained by the 

 discovery that many of the supposed Ferns were seed-bearing 

 plants, and a further explanation is suggested by the superiority 

 of seeds over stems and leaves in their adaptation to dispersal 

 by water. 



In 1874 Brongniart^ described several petrified seeds from 

 material discovered by Grand'Eury in the St Etienne coal-field, 

 and seven years later his descriptions were repubhshed*, with the 

 addition of several beautifully executed drawings, as a posthumous 

 volume edited by his distinguished pupil Renault. Wilhamson's 

 researches supphed much additional information, and in recent 

 years the more detailed study of French and Enghsh seeds by 

 Bertrand and particularly by OHver and his pupils has further 

 emphasised the interest and importance of this field of work. 

 Brongniart proposed a two-fold classification of French seeds: 

 (i) bilaterally symmetrical seeds, more or less flattened in section, 

 which he beheved to be Cordaitean; (ii) radially symmetrical 

 seeds, circular in transverse section : the latter group he considered 

 to be less closely allied to recent types. The employment of the 

 terms Platyspermeae and Radiospermeae, proposed by Oliver^ 

 for Brongniart's divisions, serves a useful purpose if due regard 

 is paid to the adequacy of the evidence as to symmetry and if 

 it is recognised that this classification cannot be rigidly employed 

 in all cases. It was pointed out by Brongniart that the occasional 

 occurrence of tricarinate seeds of Ginkgo (fig. 631) and Taxus 

 is an exception to the general rule of bilateral symmetry: seeds 

 of Cycas are normally bilateral, but radially symmetrical forms 

 also occur^. The genus Conostoma (fig. 494, B) represents an 

 intermediate type which, though almost radially symmetrical, 

 exhibits a shght tendency towards platyspermy. Evidence 



1 Williamaon (77) B. p. 262. ^ ZeiUer (88) A. p. 642. 



" Brongniart (74). * Brongniart (81). 



« OUTer (04) B. p. 389. " A£fourtit and La Riviere (15). 



