of Coal-Measure Plants. 155 



ing the question at greater length, the conclusion may be briefly 

 stated that the functions usually carried out in recent plants by 

 elements possessing the structure of phloem, were in Lepidoden- 

 droid stems performed by tissue of a somewhat different type ; 

 probably the secretory zone of the stem and the secretory elements 

 of the leaf-traces are physiologically comparable to phloem tissue, 

 and in part to the laticiferous tissues in some recent plants. 

 It has been shown by Strasburger 1 that under certain conditions 

 the xylem tissues may serve as channels for the conduction 

 of nitrogenous material ; the removal of a ring of phloem 

 from the stems of Heracleum Sphondylium did not prevent the 

 conveyance to the ripening umbel of a sufficient supply of food 

 material. In Lepidophloios it would seem probable that the 

 tissue of the secretory zone took some part in the conduction of 

 assimilated substances, but it is not wholly improbable that the 

 xylem may have also borne a share in the functions which are 

 usually associated with phloem in recent plants. It may be that 

 a more intimate acquaintance with the histology of both fossil and 

 recent Lycopodiaceous plants may demonstrate a closer agreement 

 than is admitted in the above description between the phloem of 

 recent Lycopods and the tissue which has been spoken of as the 

 secretory zone in Lepidophloios. There is, indeed, a distinct re- 

 semblance between the comparatively wide thin- walled sieve-tubes 

 and the accompanying parenchymatous elements in a Lycopodium 

 stem and the large clear spaces and associated parenchyma of 

 Lepidophloios ; but the histological similarity is not, I believe, 

 sufficient to warrant the identification of the " secretory " zone 

 of the fossil stem with ordinary phloem. 



Bibliography. 



Bary, A. de (84). Comparative anatomy of the vegetative organs of 

 the Phanerogams and Ferns. Oxford, 1884. 



Bertrand, 0. E. (91). Remarques sur le Lepidodendron Harcourtii de 

 Witham. 



Trav. et Mem. des Facultes de Lille, Mem. vi. Lille, 1891. 

 Binney, E. W. (71). Observations on the structure of Fossil Plants 

 found in the Carboniferous strata. 



Pt. ii. Lepidostrobus and some allied cones. Palaeontological 

 Soc. London, 1871. 



(72) ibid. Pt. in. Lepidodendron. Pal. Soc, 1872. 



Bower, F. 0. (93). On the structure of the axis of Lepidostrobus 

 Brownii Schimp. 



Annals Lot., Vol. vn., p. 329, 1893. 

 Brongniart, A. (37). Histoire des Vegetaux fossiles, Yol. n. Paris, 1837. 



1 Strasburger (91), p. 900. I am indebted to my friend Mr Francis Darwin for 

 calling my attention to Strasburger's experiment. 



