On the Leaf Scars of Lepidodendron, 85 



Figs. 3, 4, PI. VIII, is, at first sight, similar to that of Fig. 1, 

 PI. VIII. But it more closely resembles carinatum. The 

 spirals are steeper, hence the length of the corresponding sides 

 varies. Of course the moving or sliding of the spiral ranks 

 upon each other would change the direction of the secondary 

 spirals and the length of the sides of the scars ; and if con- 

 tinued, it would change the scars from six-sided to four-sided, 

 and back to six-sided, in constant recurrence. But this pro- 

 cess would not shorten the ends of the leaf scars. 



The proof of the identity of carinatum with aculeatum is by 

 no means confined to the locality furnishing these specimens. 

 The hexagonal form is sometimes the property of full-grown 

 leaf scars. I have observed the change from aculeatum upon 

 the same slab. Under mutual pressure, the inferior sides of 

 the leaf bases seem usually to have given way to the superior 

 sides, but sometimes the sides are all equally impressed. 



Figs. 4, 6, PI. IX, might be called L. obovatum, Sternb., which 

 Prof. Schimper has identified with L. fiternbergii, Brongt. 

 But on account of intermediate forms it is extremely difficult 

 to separate them from carinatum. If L. obovatum, Sternb., is 

 distinct from L. aculeatum, which yet admits of doubt, it is 

 Quite certain that the scars on young branches of old trees 

 would frequently be indistinguishable. 



Fig. 7, PI. IX, shows great irregularity in the shape of the 

 leaf scars. How much of the peculiarities of form in different 

 specimens may be due to decortication, or to pressure in the 

 rock, cannot be well determined. Figs. 5, 6, PI. VIII, are 

 from quite flat specimens. The absence of the more easily 

 obliterated features may be due either to rock pressure or to 

 decortication, or to both. But Figs. 3, 4, PI. VIII, are from 

 fossils having the foliar cushions in strong and clear relief. 



The vascular scar, the cicatrix of the most vital part of the 

 leaf base, is also subjeet to much variation. Its position is 

 naturally somewhat above the center of the leaf scar ; but 

 by compression and distortion of the leaf bases, the distance 

 may be either increased or diminished. The relative size of 

 the vascular scar is variable, even on the same specimen, as 

 the figures will attest. The shape varies from square to long 



