A REMARKABLE FOSSIL TREE TRUNK 335 



shown in plate 7, figure 2, or plate 9, figure i, the obliquely- 

 ascending sheaths were crowded somewhat to the side so as 

 more readily to obliterate the longitudinal seriation. 



The transition from the distinctly sigillarian arrangement of 

 the leaf cushion to the dominantly lepidodendroid type is con- 

 comitant with the relative increase of the vertical distance 

 between the leaves in the same row on the trunk; and it is 

 consequent to the more rapid longitudinal growth of the tree 

 by which the leaves are farther removed from one another in 

 the vertical sense, and the more distant sheaths are not com- 

 pactly overlapped so as to form a continuous row or ridge. 



The rectangular phyllotaxy seen in the Naples tree is in gen- 

 eral characteristic of the Devonic Lepidophytes, and is present 

 also in the Carbonic Bothrodendron (Subsigillariae). When the 

 slow longitudinal growth, without great expansion of the cortex, 

 has brought the leaf scars into very close relations vertically, 

 the leaves have in some cases been described as verticillate.^ 

 Continuous impressions of the escaping nerve-trace sheaths in 

 longitudinal rows, all the more distinctly defined through the 

 partial maceration of the softer tissues so as to form narrow 

 ribs, are also to be observed in many of the fragments reported 

 as Lepidodendron gaspianum. In the higher Car- 

 bonic Lycopods the rectangular phyllotaxy or pseudo-verticillate 

 arrangement is seen in the Sigillariae, and in the strobilar axis 

 of Sigillariostrobus, or even in Lepidostrobus. 



Leaf scar. The leaf scar of the Devonic fossil, like those 

 of the Carbonic Lepidodendron and Sigillaria is placed on the 

 upper part of the leaf cushion, and on the most prominent area 

 of the latter. In general it is very regular in form, slightly 

 obovate, or oval-obovate, rounded below and slightly cordate 

 at the upper border. Illustrations from the lower or sigillarioid 

 portion of the trunk are shown in plate 6 at S, while examples 

 higher in the specimen are seen in plates 7, 8 (in relief), and 10. 



Within the sinus at the upper edge of the leaf scar, plate 10, 

 figure 4, is a fairly distinct ligular pit, similar to that seen in 

 the Carbonic Lepidophytes. It is interesting to find the ligule, 

 so characteristic of the Paleozoic predecessors of the Lycopodiales, 

 already present in the upper Devonic type. 



The passage of the nerve trace, or vascular bundle, to the 

 leaf is marked by a punctiform scar slightly above the middle 



'e. g. Lepidodendron corrugatum var. verticillatum from the lowest 

 Mississippian. 



