930 Ml! A. C. SEWARD AND MR A. W. HTLL ON THE 



boniferous Arborescent Lepidodendron by a Study of the Details of their Organisation," ibid., vol. ix. [4], 

 p. 31, 1895. 



Williamson, W. C. (96), " Reminiscences of a Yorkshire Naturalist." (Edited by Mrs Crawford 

 Williamson.) London, 1896. 



Williamson, W. C, and Scott, D. H. (94), "Further Observations on the Organisation of the Fossil 

 Plants of the Coal-Measures. Pt. I.," 'Trans. Ro;/. Soc, vol. clxxxv. p. 863, 1894. 



— — (95), Ibid., Pt. 111., ibid., vol. elxxxvi. p. 703, 1895. 



Witham, H. (32), "On Lepidodendron Harcourtii," Trans. Nat. Hist. Soc. Newcastle-upon-Tyne, 1832. 



(33), "The Internal Structure of Fossil Vegetables," Edinburgh, 1833. 



Worsdbll, W. C. (96), "The Anatomy of the Stem of Marrozamia compared with that of other 

 Genera of Cycadese," Annals Bot., vol. x. p. 601, 1896. 



■ (98), "The Comparative Anatomy of certain Genera of the Cycadacese," Journ. Linn. Soc, vol. 



xxxiii. p. 437, 1898. 



Wunsch, E. A. (67), " Discovery of Erect Stems of Fossil Trees in Trappean Ash in Arran," Trans. 

 Geol. Soc. Glasgoiv, vol. ii. p. 97, 1867. 



Zimmermann, A. (80), "Ueber das Transfusionsgewebe," Flora, p. 2, 1880. 



EXPLANATION OF PLATES. 



[The photographs reproduced in PI. I. fig. 6, and PI. III. figs. 20 and 22, were kindly supplied by 

 Mr Kidston ; all the other micro-photographs have been taken by Mr W. Tains, Cambridge.] j 



Plate I. 



Fig. 1. Transverse section of the stem. />, pith ; x, primary wood ; x, secondary wood. Circ. \ nat. 

 size. 



Fig. 2. Portion of the outermost cortex, mainly composed of phelloderm, which extends from b to the 

 surface of the stem, a, position of a leaf -trace ; b g, regions referred to in the text. Nat. size. 



Fig. 3. Longitudinal section of a secretory strand in the phelloderm. x 100. 



Fig. 4. Longitudinal section of the pith, and portions of two xylein tracheids. x 100. 



Fig. 5. Longitudinal section through the edge of the secondary wood, t', narrow tracheids ; t" , 

 thinner and shorter elements representing partially developed tracheids ; mr, medullary ray. x 80. 



Fig. 6. Part of a medullary ray as seen in a transverse section of the secondary xylem. x 190. 



Fig. 7. Tangential section of the secondary wood, showing a broad medullary ray and a leaf-trace, It. 

 x90. 



Fig. 8. Tangential section of the phelloderm showing a mass of parenchyma (parichnos) cut through 

 transversely. x 80. 



Platk II. 



Fig. 9. Transverse section of the secretory zone. Sc. an, outer portion of the meristematic region. 

 xlOO. 



Fig. 10. Radial longitudinal section, slightly oblicpie, of the outermost portion of the secondary xylem 

 and neighbouring tissue. it and t" , new and partially developed tracheids ; cm, meristematic tissue. 

 x80. 



Fig. 11. Transverse section of the secondary wood, showing a group of smaller tracheids. t, tiillen in 

 the cavities of two tracheids. x 120. 



Fig. 12. Transverse section of the phelloderm, with a row of secretory cell-groups. x 80. 



Fig. 13. Radial longitudinal section through the junction of the primary and secondary xylem 

 (x and x"). x 90. 



Fig. 14. Radial longitudinal section through the phelloderm, passing through a leaf-trace with partially 

 disorganised tracheids tr and the parichnos pr. x 60. 



Fig. 15. Transverse section through the stelar region and the outer edge of the secondary wood. 

 /, leaf-traces ; sc, secretory zone. x 50. 



