of Coal- Measure Plants. 157 



Williamson, W. C. (93 2 ). General, Morphological and Histological 

 Index to the Author's Collective Memoirs on the Fossil Plants 

 of the Coal-Measures. Pt. II. 



Mem. Proc. Lit. Phil. Soc. Manchester, Vol. vil. [4], p. 1, 

 1893. 



(95)- On ^ ne light thrown upon the question of Growth 



and Development of the Carboniferous Arboi'escent Lepidodendra 

 by a study of the details of their organisation. 

 Ibid, Vol. ix. [4], p. 31, 1895. 

 Witham, H. (32). On Lepidoden do-on Harcourtii. 



Trans. Ra,t. Hist. Soc. Newcastle-upon-Tyne, 1832. 



(33). The internal structure of fossil vegetables. 



Edinburgh, 1833. 



Explanation of Plates. 



Plate III. (Microphotographs by Mr W. Tarns, Cambridge.) 



Fig. 1. Transverse section of a leaf-trace in the middle cortex, x = xylem ; 

 s = secretory tissue. (Slide 3.) x 50. 



Fig. 2. Transverse section of a leaf-trace in the outer cortical region. 



p — parichnos ; c = outer cortex ; s ~ secretory tissue, partially 



disorganised; x = xylem. (Slide 3.) x 50. 

 Fig. 3. Transverse section through the edge of the corona (primary 



xylem of the stele) and the secretory zone (s). x = primary xylem ; 



a = meristematic zone; It 1, It 2 = leaf-traces. (Slide 1.) x 50. 

 Fig. 4. Longitudinal section through the tissues shown in fig. 3. 



(Slide 4.) x 50. 

 Fig. 5. Oblique section of a leaf-trace, x = tracheids ; s = secretory 



tissue. (Slide 2.) x 50. 



Plate IV. 

 Fig. 6. Transverse section of the outer cortex. PI = phelloderm ; 

 sc = group of secretory cells. (Slide 2.) x 90. 



Fig. 7. Transverse section of the tracheids of a leaf-trace as seen near 

 the corona. Px = protoxylem. (Slide 3.) x 100. 



Fig. 8. Transverse section, showing a few of the innermost tracheids 

 of the primary xylem of the stele and a single short reticulate tracheid 

 next the meristematic cells of the pith. ('Slide 1.) x 200. 



Fig. 9. Longitudinal section of a leaf -trace. x = xylem tracheids ; 

 s = elements of the seci-etory strand. (Slide 2.) x 50. 



Fig. 10. Transverse section through the junction of the lacunar middle 

 cortex and the thicker walled cells of the outer cortex. (Slide 3.) x 100. 



Fig. 11. Longitudinal section through part of the secretory zone of a leaf- 

 trace, showing some of the cells with dark contents. (Slide 4.) xlOO. 



Fig. 12. Transverse section of the secretory zone; the outermost 

 (uppermost) layer of cells is probably the endodermis. (Slide 1.) xlOO. 



VOL. X. PT. III. 12 



