A REMARKABLE FOSSIL TREE TRUNK 337 



less a well developed Lycopod, and not the most simple in its 

 organization. It is even possible that it developed secondary 

 wood in the dilated butt. 



Its base was provided with stigmarioid rootlets and was pre- 

 sumably supported by some type of stigmarioid root, though 

 the other contemporaneous Devonic material yet found does 

 not justify the assumption that it was associated with the long 

 roots typical of Stigmaria. 



We have seen that the leaf cushion form in the lower portion 

 of the trunk is characteristic of the favularian ribbed Sigillariae, 

 while that higher on the trunk is equally characteristic of the 

 Lepidodendreae. The leaf cushions differ, however, from Lepi- 

 dodendron by the phyllotaxy ; from Sigillaria by their narrowly 

 rhomboidal form ; and from Bothrodendron by the development 

 of ribs and definite leaf cushions which, in conjunction with the 

 relative linear or lateral growth of the axis, results respectively 

 in the lepidodendroid or the sigillarioid aspect of cortex. 



The costae are due to the vertical alinement of the cushions 

 and the presence of a resistant nerve trace sheath which trav- 

 erses the cortical tissue and which becomes imbricated in a 

 longitudinal ridge when the surrounding tissues have shrunken. 

 Partial decortication displays these sheaths as a Knorria con- 

 dition, a condition found in Lepidodendron, Bothrodendron and 

 Asolanus (Subsigillariae). 



By its leaf scars the Naples tree is most closely related to 

 Bothrodendron and the Rhytidolepis Sigillariae. It differs from 

 the former by its elongated parichnoi and from the latter by 

 its obovate form. On the whole it is nearly intermediate to 

 the two groups. 



The leaves of the fossil trunk are in character nearest those 

 of Bothrodendron, especially in respect to their basal dilation, 

 though in aspect they closely resemble those of certain Lepi- 

 dodendra. The persistence of the leaves is characteristic of the 

 Devonic group to which the trunk belongs. 



Although this group has nearly always been described as 

 Lepidodendron, its special resemblance to the latter is confined 

 to the development of narrowly rhomboidal prominent leaf 

 cushions and to the habit of the leaves. Bothrodendron some- 

 times exhibits distinct rhomboidal leaf cushions^ in the small 

 twigs though its cortical surface is flat and shagreened in the 

 larger members. In the Sigillarian group the nearest relatives 



iSee Weiss & SterzeL Die Gruppe der Subsigillarien. 1803. pl-i. fig- 3- 



