XXXV] RHABDOSPERMTJM 343 



carpus are transferred by Arber to his genus Platyspermum 1 , a 

 designation for which it is proposed to substitute Nathorst's 

 genus Holcospermum 2 . In seeds preserved as more or less 

 flattened impressions it is practically impossible in many cases 

 accurately to determine the symmetry : as fig. 506, A, shows, 

 casts indistinguishable from some examples of Platyspermum are 

 radially symmetrical. Brongniart 3 extended the original defini- 

 tion of Rhabdocarpus to include certain anatomical characters, and 

 these have been more fully defined by Bertrand 4 . It is for seeds 

 showing these anatomical features that the name Rhabdospermum 

 is now proposed. This course is followed on the ground that it 

 is advisable to avoid confusion between petrified specimens and 

 impressions which in spite of superficial resemblance may not be 

 closely related. In some cases it is practically certain that an 

 impression of the Rhabdocarpus type is generically identical with 

 a seed of similar form showing the anatomical structure of Rhabdo- 

 spermum, but unless identity is established a distinct terminology 

 is preferable. The use of the generic name Rhabdospermum 

 carries with it an implication of platyspermy, but under Rhabdo- 

 carpus may be included seeds which are radiospermic and platy- 

 spermic. Some seeds agreeing with Rhabdospermum are referred 

 by Grand' Eury 5 to Poroxylon, and it is probable that Rhabdo- 

 spermum like Cardiocarpus is a Cordaitean seed. On the other 

 hand Rhabdocarpus may well include species, apart from those 



1 In selecting a generic name for a fossil plant or part of a plant it has not 

 been the universal practice to avoid the use of a designation previously employed 

 for a recent plant. It is clearly in accordance with the Rules adopted by the 

 International Botanical Congress and with general convenience to avoid the 

 employment of the same name for two different generic types even if one is known 

 only in a fossil state. My attention has been called by Mr W. N. Edwards of the 

 British Museum to the fact that the names Platyspermum, Microspermum, and 

 Pterospermum recently proposed by Dr Arber for Palaeozoic seeds have previously 

 been given to recent flowering plants. Though I have often neglected to consult 

 the Index Kewensis and the Genera Siphonogamarum before proposing a 'new' 

 generic term, I fully recognise the importance of avoiding the employment of names 

 in current use or names which have 'lapsed into synonymy*.' 



2 See page 361. 



3 Brongniart (74) p. 246; (81) p. 21, Pis. ix. xi. 



4 Bertrand, C. E. (07). F > Grand'Eury (05). 



* Regies internationales de la nomenclature botanique adoptees par le Cong. 

 Internat. Bot. de Vienne, 1905, etc. T. Briquet, Jena, 1912, p. 37. 



