STRUCTURE AND AFFINITIES OF A LEPIDODENDROID STEM. 919 



his possession, but no diagnosis of the plant is given. In 1871 Binney * described 

 three new Lepidostrobi from the Arran volcanic beds, and to one of these, a hetero- 

 sporous form, he gives the name Lepidostrobus Wiinschianus. In 1880 Williamson 

 published an account of the Arran Lepidodendron,t in which he described and figured 

 small twigs with a solid " vascular axis " (stele), and larger branches and stems with a 

 parenchymatous axial region enclosed by a ring of wood. He regarded the smaller 

 specimens as representing different stages in the growth of the large trunks, and dis- 

 cussed the evidence in favour of a gradual increase in diameter of the axial tissues, and 

 the conversion of a solid vascular stele to a larger stele with a central parenchyma. In 

 1883 the same author \ gave an account of an Halonial branch from Arran which with 

 good reason he referred to the plant previously described. Ten years later Williamson 

 made a brief reference to Binney's Arran Lepidostrobi, and in the second part of his 

 Index, § published in that year, he speaks of the Laggan Bay plant as Lepidodendron 

 Wiinschianum (Will.), having hitherto refrained from the use of a specific name in 

 dealing with the " Arran Lepidodendron." Finally in 1895 Williamson || gave a 

 summary of his work on this species, and again discussed the question of growth and 

 modification of the stele during the development of the stem. 



Solms-LaubachU has dealt at some length with Williamson's views on the growth 

 of the Arran stems, and points out the physical impossibilities involved in some of the 

 suggested explanations of the conversion of small solid steles into large steles with a 

 wide centra] parenchyma. We must regard the various forms described by Williamson 

 as representing, in part at least, branches of different orders, but all belonging to one 

 specific type. 



In a footnote to a paper in which some account is given of the Arran species, 

 Kidston ## adds that the plant should be referred to the genus Lepidophloios and not to 

 Lepidodendron, if Williamson was correct in connecting the Halonial branches which he 

 described in 1883 with the large Laggan Bay trunks. ft 



It would necessitate an unreasonable extension of the paper to discuss in detail and 

 to illustrate by drawings the numerous points of interest as regards the comparative 

 anatomy of the Lepidodendrese which are suggested by an examination of the Dalmeny 

 specimen. There are certain considerations, however, which must be briefly touched 

 on, as they have a direct bearing on the question of the systematic position of the 

 plant. To deal first with the Arran plant, which should be designated Lepidophloios 

 Wiinschianus. 



The large stems represented by various sections in the British Museum J| and in the 

 Binney Collection, Cambridge, and by a magnificent specimen in the Owens College 

 Museum, agree closely in size as well as in structure with the Dalmeny fossil. There 



* Binne? (71), p. 56, pi. xi. t Williamson (80). J Ibid. (83), p. 466. 



§ Ibid. (93), p. 15. || Ibid. (95), p. 43. 



1 Solms-Laubach (91), p. 229. Vide also Bertrand (91), p. 40. ** Kidston (97), p. 40. 



tt For the evidence in favour of the connection between Halonial branches and Lepidophloios, vide Kidston (93), 

 pp. 539 et seq. J J E.g., sections Nos. 451, 452, etc. 



