On the Leaf Scars of Lepidodendron. 81 



in one vertical rank, or w 1 "Ja normally should be so con- 

 nected. The breaks in the connecting lines on either side of 

 scar number one, in Fig. 1, PI. Y, and also between scars four 

 and two, in Fig. 2, have evidently been produced by expansion 

 and consequent cracking. But between leaf scars four and 

 six, and in two other places on the right side of Fig. 2, PI. Y, 

 the lines were either destroyed or prevented from ever appear- 

 ing by the crowding of the leaves. 



If the compression of the leaf scars is still greater, the 

 overlapping ends of the scars will be so shortened as merely 

 to meet. This is the condition represented by L. modulatum, 

 Lesq. Fig. 4, PI. YI, is after the original figure. In this 

 stage of compression, two scars belonging to adjacent series 

 are brought end to end, and apparently connected ; two 

 naturally alternate margins are brought together ; leaf scars 

 which properly should be separated by two intervening series 

 are brought side bj r side ; and all the scars are consequently 

 much shortened. Fig. 3, PI. YI, is a form transitional be- 

 tween aculeatum and modulatum, showing the overlapping 

 ends not entirely destroyed. In this coarctate form, the leaf 

 scars are somewhat confluent. This condition is very com- 

 mon, much more so than the perfect modulatum. 



It may be claimed that the relation of the leaf scars is 

 essentially the same in modulatum as in Figs. 1, 5, PI. YI, 

 or Figs. 1, 2, PI. Y, and that the difference is only in the 

 proportions of the scars and the length of the connecting 

 line. This is true of some specimens ; and yet the form is 

 abnormal. The bases of the leaves assumed this form under 

 compulsion ; it is the second degree of compression of the 

 typical form. There is a perfect transition from the typical 

 form to modulatum, through the form first called aculea 

 turn, by many minute gradations ; and the positive proof 

 is, that aculeatum is present in most specimens of the ty- 

 pical form, and modulatum is frequently shown on slabs of 

 aculeatum. The form modulatum exists in the specimen 

 from which Fig. 2, PI. YI, is taken. Such examples are 

 found in most collections. In many specimens of modulatum, 

 the line joining the leaf scars is evidently not a continuation 

 1877. 6 Ann. N Y. Acad. Sci., Vol. I. 



