of Coal-Measure Plants. 141 



applied to the dark brown elements accompanying the tracheal 

 strand of the leaf-trace, and I have no hesitation in expressing the 

 view that Bertrand's suggestion of the secretory nature of these 

 elements is nearer the truth. This is, however, a matter of 

 secondary importance as regards the supposed distinction between 

 L. fidiginosum and L. Harcourtii afforded by the duplex nature of 

 the leaf-traces ; one of the conclusions, based on a comparative 

 examination of specimens of both species, is that no such difference 

 exists, but on the contrary the structure of the leaf-traces in the 

 two species is practically identical. 



As Williamson pointed out, the true Lepidodendron Harcourtii 

 differs from L. fuliginosum in the absence of the middle cortical 

 tissue ; that is to say, the former species possessed a cortex largely 

 composed of very delicate cells which were always wholly or 

 partially destroyed before the mineralising solution had time to 

 effect their preservation ; in L. fuliginosum, on the other hand, 

 the corresponding region of the stem was occupied by a mass of dark 

 coloured parenchyma which, in view of its frequent preservation, 

 was probably of a more resistant nature than in L. Harcourtii. 

 To found specific distinctions on accidents of preservation is 

 naturally dangerous, but this difference in the cortical tissues is 

 sufficiently constant to entitle it to careful consideration, and 

 although we have evidence pointing to the existence of a similar 

 cortex in both species, it would seem probable that in L. fuliginosum 

 the bulk of the cortical region consisted of firmer and more durable 

 tissue. In the Binney sections referred to L. Harcourtii the cortex 

 is well preserved ; in this respect, therefore, as in others, they agree 

 with L. fuliginosum. 



Another point of importance is the absence or late develop- 

 ment of secondary vascular tissue in the true L. Harcourtii; in 

 Binney 's sections there are distinct traces of the development in 

 its early stages of a secondary stelar tissue which agrees with the 

 corresponding tissue in L. fuliginosum. In a recent account of a 

 large Lepidodendroid stem from the Calciferous Sandstone of 

 Dalmeny in South Scotland by Mr A. W. Hill and myself 1 , the 

 opinion is expressed that this large stem, with a considerable 

 development of secondary wood, may perhaps be regarded as an 

 example of Lepidodendron Harcourtii. Be this as it may, it is 

 undoubtedly true that smaller examples of this species are 

 characterised by the absence of any secondary xylem. 



Williamson and others have referred to the greater prominence 

 of the projecting ridges on the external face of the primary xylem 

 (corona) as one of the distinguishing features of L. Harcourtii ; but 

 it is doubtful how far this character can be accepted as of diagnostic 



1 Seward and Hill (99); Seward (98), p. 82, fig. 15. 

 VOL. X. PT. III. 11 



