XXXIII] CORDAITES 225 



investigation. The plants of the present age are to a large extent 

 the result of evolutionary tendencies more correctly described 

 as the result of degeneration or simplification than as the latest 

 phase in a series composed of a succession of types gradually 

 growing in complexity. Cordaites is essentially a generalised 

 type, a composite product of an age characterised by an activity 

 in the elaboration of the complex from the simple. Botanical 

 records furnished by the geological series available for investigation 

 furnish evidence of the sorting of characters among gradually 

 diverging races and of changes in plant-organisation tending 

 towards simplification and increased efficiency. 



Cordaites, using the generic designation in a wide sense, occurs 

 in Carboniferous and Permian strata in Europe, North America, 

 and China; it is recorded from several localities in Russia and 

 Siberia for the most part from Permian rocks, from Permo-Car- 

 boniferous (Lower Gondwana) beds in India, Australia, South 

 Africa, and South America. Wood agreeing generally in the 

 structure of its secondary tracheids with that of Cordaites is 

 represented in Devonian rocks, and there can be no doubt as to 

 the existence of Cordaitalean plants in pre-Carboniferous floras. 

 It is represented in the Rhaetic flora of Tonkin and has recently 

 been discovered in strata probably of Rhaetic age in Mexico. 



LEAVES. 



It is important to recognise the fact that leaves included 

 under the generic name Cordaites were in many cases not. borne 

 on stems or branches with the anatomical characters of Cordaites. 

 Scott in his account of the genus Mesoxylon says, * I feel no doubt 

 that most of the British specimens of Cordaitean leaves really 

 belong to Mesoxylon, which is a much commoner type of stem 

 in the Coal Measure petrifications than that of Cordaites itself 1 .' 

 Some of the Cordaitean leaves were probably attached to stems 

 of the Poroxylon type 2 and it is not improbable that, as investi- 

 gations are extended, additional genera of vegetative shoots will 

 be discovered provided with leaves similar at least in external 

 characters to those which it is customary to refer to Cordaites. 

 In the present state of our knowledge we cannot make use of 



1 Scott (12) p. 1024. 2 Grand'Eury (05). 



s. m 15 



