44 Transactions. 



projecting neck of four tiers of cells, which in most cases in the mature 

 organ falls off almost level with the surface of the prothallus. In figs. 7 

 and 8 he shows two stages in the development of the antheridium. He 

 gives no account of the embryo in this second paper, but leaves this 

 subject for a still further communication. 



In the same paper Professor Lawson describes and figures the pro- 

 thallus and sexual organs of Psilotum. Here again his description is 

 based upon ample material. There is no need for me to go into any detail 

 other than to notice that Lawson draws attention to the remarkably close 

 similarity between the prothalli and sexual organs of the two genera. 

 This similarity in the matter of the gametophyte generation hears witness 

 to the very near affinity of Psilotum with Tmesipteris, and serves also to 

 draw our attention to the fact of the essential similarity in the stelar 

 anatomy of the sporophyte. Lawson notes that the prothallus of Psilotum 

 as described by him differs wholly from that which Lang provisionally 

 assigned to Psilotum. 



I have not seen Darnell-Smith's paper on the gametophyte of Psilotum 

 {Trans. Roy. Soc. Edin., vol. 52, 1917), quoted by Professor Lawson, in 

 which he gives his observations on the germination of the spore, so cannot 

 compare what he there says concerning the first-formed part of the 

 prothallus with what I have described in the present paper in various 

 well-grown prothalli with regard to the same. 



Literature consulted. 



Boodle, L. A., 1904. On the Occurrence of Secondary Xylem in Psilotum, Ann. Bot., 



vol. 18, pp. 505-17. 

 Bower, F. 0., 1894. Studies in the Morphology of the Spore-producing Members, 



I. Equiset. and Lycopod., Phil. Trans. Roy. Soc. Lond., ser. B, vol. 186. 



1908. The Origin of a Land Flora, London. 



Brttchmann, H., 1898. fiber die Prothallien und die Keimpjtanzen mehrerer europiiischer 



Lycopodien, Gotha. 

 Campbell, D. H., 1911. The Eusporangiatae — The Comparative Morphology of the 



Ophioglossaceae and Marattiaceae, Washington. 

 Cheeseman, T. F.. 1906. Manual of the New Zealand Flora. Wellington. 

 Engler. A., and Prantl, K-. 1900. Pflanzenfamilien. Teil 1, Abteihmg iv, Psilo- 



taceae. 

 Ford, Miss S. O.. 1904. The Anatomy of Psilotum triquetrum. Ann. Bot.. vol. 18, 



pp. 589-605. 

 Kidston, R., and Lang, W. H., 1917. On Old Red Sandstone Plants, showing 



Structure, from the Rhynie Chert Bed, Aberdeenshire, Pt. i, Rhynia Givynne- 



Vaughani, Trans. Roy. Sic. Edin., vol. 51, pt. 3, No. 24. 

 Lang, W. H., 1902. On the Prothalli of Ophioglossum pendulum and Helminthostachys 



zeylanica, Ann. Bot., vol. 16, pp. 23-56. 

 1904. On a Prothallus provisionally referred to Psilotum, Ann. Bot., vol. 18, 



pp. 571-77. 

 Lawson, A. A.. 1917a. The Prothallus of Tmesipteris tannensis, Trans. Roy. Soc. 



Edin., vol. 51, pt. iii, pp. 785-94. 

 — — 1917b. The Gametophyte Generation of the Psilotacea*?, Trans. Roy. Soc. Edin., 



vol. 52, pt. i, pp. 93-113. 

 Scott, D. H., 1909. Studies in Fossil Botany, 2nd ed. (1st ed. 1900), London. 

 Seward, A. C, 1910. Fossil Plants, vol. 2, Cambridge. 

 Sykes, Miss M. G., 1908. The Anatomy and Morphology of Tmesipteris, Ann. Bot., 



vol. 22, pp. 63-89. 

 Thomas, A. P. W., 1902. The Affinity of Tmesipteris with the Sphenophyllales, Proc. 



Roy. Soc, vol. 69, pp. 343-50. 

 Tretjb, M., 1884-90. Ktudes sur les Lycopodiacees, Ann. duJard. bot. de Buit. (Refer- 

 ences in standard works.) 



