50 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



The rhizome of Lepidodendron is Stigmaria, but as Stigmaria 

 is also the rhizome of Sigillaria, if not also of other Arborescent 

 Lycopods, it will be considered separately. 



The genus Knorria, Sternberg, 1 is founded on a decorticated 

 condition of Lepidodendron, and other Lycopod stems. It 

 arises in this way. The inner tissues having decayed, the firm, 

 outer portion of the bark is left as a hollow cylinder. When this 

 has become filled with sediment and subjected to pressure, the 

 contained infilling material is pressed into the openings in the 

 outer bark, through which the vascular bundles pass to the 

 leaves. On the subsequent decay of the bark, the casts of the 

 bundle passages are left as so many spine-like points attached to 

 the central inorganic core which filled up the hollow cylinder. It 

 must be remembered that these passages not only represent the 

 space occupied by the leaf-bundle, but also the cellular sheath 

 which accompanied it, and which divided out two arms when in 

 the leaf-cushion to form the parichnos. 



I possess an interesting specimen of which the core is Knorria 

 acicularis, 2 but the impression on the rock which surrounded the 

 Knorria is Lepidodendron Veltheimianum, Sternb. The space 

 between the Knorria and the Lepidodendron was filled in with 

 coaly matter when found (Nos. 50-51). 



There remains still to be considered the question of the affinity 

 of Lepidodendron. 



That it is Lycopodiaceous is clearly shown from the develop- 

 ment of the sporangium, but as to which of the existing genera 

 of Lycopods Lepidodendron stands closest is a very difficult point 

 to determine. 



In the structure of the vascular axis perhaps it stands closer to 

 Lycopodinm than to Selaginella. Some Lepidodendra are 

 certainly heterosporous, though some species may have had 

 homosporous cones, but on this point there is at present no 

 certainty.' 3 The known heterospory of at least some Lepido- 

 dendra point to closer affinities with Selaginella than with 



1 Sternberg, Flore monde prim., Vol. I., fasc. IV., p. 37, 1826. 



2 Knorria acicularis, Goppert, Die fos. Flora des Ubergangsgebirges, p, 

 200, PI. XXX., fig. 3, 1852. 



3 See remarks under Lepidostrobus, p. 61. 



