654 STUDIES IN FOSSIL BOTANY ■ 



The Araucarieae present a close agreement with the 

 Cordaiteae in the structure of the stem, and especially 

 in that of the wood, which, as universally admitted, is 

 often indistinguishable in the two families. The essen- 

 tial feature is that the mass of the wood, apart from 

 the medullary rays, is composed of tracheides with 

 multiseriate bordered pits on their radial walls. This 

 is the characteristic type of wood throughout the 

 Cordaitales and Pteridosperms, extending also (in the 

 form of primary xylem) to many of the older Ferns, 

 while it is practically unknown among Lycopods, 1 in 

 which the tracheides are very constantly scalariform. 

 The absence of centripetal wood in the Araucarian 

 stem presents no difficulty on the hypothesis of 

 Cordaitean affinity, for its gradual disappearance in 

 certain Pteridosperms and in the older Cordaitales 

 can be traced, until it is lost in the stems of the 

 typical Cordaiteae. No such links with the stem- 

 structure of Lycopods are known. 



The roots in Araucarieae (and Conifers generally) 

 are essentially of the same type as in Cordaitales, and 

 show none of the peculiarities of Lycopod roots. 



The leaves of Araucarieae, with their numerous 

 parallel bundles, agree generally, though not in detail, 

 with those of Cordaiteae. That the multinervate 

 character is primitive is indicated by the fact that the 

 cotyledons likewise contain several bundles. Lycopods 

 as a rule have only one foliar bundle, which, in the case 

 of Sigillariopsis, divides into two. If the Araucarieae 



1 The only case I know of is in Renault's Sigillariopsis Decaisnei, where 

 some of the tracheides are pitted, though they do not appear to agree at all 

 closely with those of the Araucarieae. 



