104 Proceedings of the Boyal Physical Society. 



the bark, which are more hexagonal in outline (PI. II., Figs. 

 2 and 3, /). In longitudinal section they are elongated, 

 and have a similar appearance to the true camhium in 

 dicotyledons (PL IL, Fig. 1, /). This has been called the 

 tubular portion of the outer bark, by Professor Williamson. 

 The meristem layer is usually ruptured, a character noticed by 

 several writers on these stems. This rupturing is what might 

 be expected from the delicate nature of the meristem cells. 



The meristem layer is surrounded by the external layer of 

 the bark in connection with the leaf bases, and is composed 

 of parenchyma, similar to the ground mass of the leaves 

 (PL II., Figs. 1 and 2, g). 



A true epidermis is wanting in these plants, the whole 

 exterior surface being covered by the persistent leaf bases 

 (PL II., Figs. 1 and 2, h). 



The leaves of Lepidodendron seem to have had an articula- 

 tion a short distance above the base, at which point the 

 upper portion of the leaf separated, the base being persistent 

 for a longer or shorter time. These persistent leaf bases are 

 well shown in the longitudinal sections of this specimen. 

 This is a matter of great importance to systematists, the per- 

 sistence of the leaf bases being one of the chief characters on 

 which Sternberg founded his genus Lepidophloios, a genus 

 which most authors are now inclined to unite with Lepi- 

 dodendron.* 



From the foregoing remarks, the structure of Lepidodendron 

 selaginoides may be said to consist of a central vascular bundle 

 (PL IL, Figs. 1 and 2, a, and PL II.«, Fig. 2, a), surrounded 

 by a delicate parenchymatous sheath of considerable thick- 

 ness (PL IL, Figs. 1, 2, and 5, c, and PL ll.a, Fig. 2, c), outside 

 of which we have the bark (PL IL, Figs. 1 and 2, d), which 

 receives constant additions from a layer of meristem (PL IL, 

 Figs. 1 and 2, /) ; and immediately outside of this we have 

 an external layer (PL IL, Figs. 1 and 2, g), in direct relation 

 with the leaf bases (PL IL, Figs. 1 and 2, h). 



Professor Dickson, to whom I have shown my preparations, 

 has expressed his concurrence with my determination of the 



* Carruthers — Monthly Mic. /oj^nift^, January 1872. Williamson, "On 

 the Organisation," etc., Phil. Trans., June 1871. 



