A REMARKABLE FOSSIL TREE TRUNK 333 



in the segment extending to 325 cm shown in plate 11. In this 

 region the leaf cushions are elongated, close, indistinctly fusi- 

 form, more prominent at the upper end, asymmetrical, and 

 distinctly spirally arranged. In other words, so far as concerns 

 form and topography the leaf cushion is nearly typical of 

 Lepidodendron. 



Knorria condition of cortex. An interesting feature presented 

 by the Naples tree is the existence of a region of Knorria con- 

 dition^' at about 225 cm from the base. This is shown in an 

 area, plate 10, figure i, in which, on the right, we see the broken 

 remains of the elongate, narrow-rounded nerve trace sheaths 

 passing nearly erect upward and outward to the underlying 

 and concealed surface of the bark, those below being imbricated 

 over those emerging higher in the trunk. The fragments still 

 adhere to the impression of the outer cortex, their broken, inner 

 ends projecting downward. Where removed, a little to the 

 left of the middle, we see the narrow leaf costation, which 

 toward the border, still further to the left, yields to the lepi- 

 dodendroid type of cushion. It will be noted that the sheath 

 casts appear to widen upward to the full breadth of the rib. 

 In the area partially shown in figure 2, in the same plate, we 

 see the expression of these sheaths very obliquely emerging to 

 the narrowly rhomboidal or fusiform cushions, and passing to 

 the leaf scars themselves. The Knorria stage or structural type 

 is known in the cortices of Lepidodendron, Bothrodendron, and 

 the Asolanus group, or Subsigillariae. 



Phyllotaxy of the tree. The seemingly anomalous occurrence 

 of the favularian (sigillarian) costate type of leaf cushion in 

 one part and of the lepidodendroid type in another part of 

 the same individual trunk finds its explanation in the Knorria 

 stage just described and in the character of the disposition 

 (phyllotaxy) of the leaf cushions on the trunk. 



The plan of the leaf cushion distribution is well shown in 

 figures I and 2, plate 7, or any of the other areas in the lower 

 part of the trunk. In the portions cited we find a very dis- 

 tinct alinement in vertical rows, a fairly clear horizontal aline- 

 ment, and less conspicuous oblique rows at an angle of approxi- 

 mately 45°. The scars alternate in the transverse rows which 

 are at an angle averaging very nearly 90° with the longitudinal 



'^The name Knorria was applied to a Lepidodendron cortex in which, as the result of partial 

 maceration of the tender tissues of the inner and middle cortexes, the casts of the leaf trace 

 sheaths, spirally arranged and usually very oblique or appressed, are shown as imbricated scale 

 points, in aspect suggesting spirally placed erect slivers. It was at first regarded as a valid 

 genus, but wa'i later recognized as merely a condition of preservation of certain lepidophytic 

 stems. 



