TRUNCI. 117 



the same necessity for a more comprehensive class designation is 

 equally apparent in the case of cycad-like stems. It would be 

 impossible to so far extend the present limits of the Cycadacece, as 

 to incorporate under that term all the fossil stem structures in 

 which characteristic features of cycadean anatomical structure 

 have been recognized ; but we must in any case clearly under- 

 stand that such stems as Bennettites and others, although very 

 closely related to recent cycads in histological details, are, 

 however, separated from living forms by certain peculiarities 

 in the morphology of their reproductive organs. The above 

 heading, therefore, of Trunci does not exclude such stems as 

 are known to be associated with a bennettitean form of floral 

 structure ; it must be taken in a more comprehensive sense than 

 merely including stem structures which agree in all essential 

 features with living members of the Cycadece or Zamiece. 



The study of cycadean stems has been raised to considerable 

 importance by the fact of the preservation, in several instances, 

 of more or less perfect internal structure in fossil specimens. 

 As with fronds, so here again we are debarred from any complete 

 diagnoses of many fossil stems by the isolated occurrence of the 

 leaves and their supporting axes. We must for the present 

 restrict ourselves to an investigation of facts as regards the 

 anatomy of stem structures ; and, as in Bennettites, of the 

 accompanying floral shoots. 



The early records of so-called cycadean stems in Palaeozoic 

 rocks have already been referred to. It is often a matter of 

 some considerable difficulty to confidently identify a structureless 

 cast or impression of a cycadean trunk ; the imperfectly preserved 

 stems of some forms of Sigillaria, Lepidodendron, or Lepidofloyos 

 may simulate fairly closely the characteristic appearance of 

 cycadean stems. In Grand'Eury's recent monograph on the 

 Coal-field of Gard there is a figure of Lepidofloyos laricinus, 

 Sternb., 1 which may be reasonably compared to a stem of 

 a cycadean plant, bearing lateral appendages suggestive of a 

 bennettitean inflorescence. The tree fern genus Protopteris, with 

 its leaf-trace bundle scars imperfectly shown or apparently 

 absent, may be mistaken for a cycadean axis with its prominent 



1 Grand' Eury (1), pi. vi. fig. 17. 



