224 COEDAITEAE [CH. 



Araucarioxylon for wood of the same type differing only in 

 geological age is an argument in favour of extending Dadoxylon 

 to all specimens having certain anatomical characters, which 

 cannot be certainly assigned either to the Araucarineae or the 

 Cordaitales, irrespective of geological age. The term Cordaidadus 

 sometimes applied to branches is hardly necessary, but the sub- 

 generic names Eu-Cordaites, Dory -Cordaites, and Poa-Cordaites, 

 instituted by Grand' Eury for different forms of leaf, are frequently 

 employed and serve a useful purpose as descriptive terms though 

 the characters which they connote are of small importance and 

 by no means always well defined or constant. For inflorescences 

 it is customary to adopt the name Cordaianthus suggested by 

 Grand' Eury as a substitute for Aniholiihus and some other terms. 

 The same author uses Rhizo-Cordaites for roots. 



The nomenclature of seeds is more difficult : in a few instances 

 seeds occur in organic connexion with Cordaitean shoots, but 

 there is no doubt that many platyspermic Palaeozoic seeds 

 preserved as detached fossils belong to Cordaites or some other 

 member of the group. The difficulty is that in the present state 

 of knowledge we cannot definitely determine in many cases whether 

 a seed is Cordaitean or whether it belonged to a genus of Pterido- 

 sperms. For this reason the account of several seeds that were 

 probably borne on Cordaites or some allied genus is given in a 

 later chapter devoted to Gymnospermous seeds. There is no 

 doubt that under the generic names Cardiocarpus, Cordaicarpus, 

 and Samaropsis are included true Cordaitean seeds, though it 

 would be incorrect to say that all the seeds so named belong to 

 members of the Cordaitales. 



Cordaites reached its maximum development in the Carboni- 

 ferous and Permian periods; the genus or some closely allied 

 types persisted into the Triassic and Rhaetic periods, and there 

 is reason to believe that the group was represented in some post- 

 Rhaetic floras. The genus is one of many remarkable examples 

 of the high degree of specialisation attained by Palaeozoic plants. 

 The complex mechanisms represented by Cordaites and similar 

 types give force to the conviction that we cannot hope to penetrate 

 below the higher branches of the genealogical tree which had its 

 roots in a period of the earth's history inaccessible to botanical 



