422 Transactions. 



is stilHmore unspeeialized in its origin, arising as a lateral branch from the 

 rhizome just as do the aerial shoots in the older state. The alternation 

 of fertile with sterile zones on the aerial branch is not a fixed character, 

 a branch being zoned or practically altogether fertile according to its habit 

 of growth. Neither the sporophyll nor the sterile leaf is fixed in form. 

 Thus the Tmesipteris sporophyte is a peculiarly unspecialized plant-body 

 not only in the absence of cotyledon and root organs from the embryo, 

 but also in the general organization of the rhizome and of the aerial shoot. 

 In their description of the rootless and leafless Rhyniaceae, Kidston 

 and Lang express the opinion that this simple plant-body " might as well 

 be termed a cylindrical branched vascular thallus as a stem " (9, p. 619). 

 They are more inclined to interpret it in the light of the theory that 

 the sporophyte of the higher plants has arisen by modification and by 

 specialization in the time of appearance of the asexual stage of an algal 

 ancestor, rather than as the result of the adoption of an independent 

 existence by a sporogonium-like ancestor with the consequence of a pro- 

 gression in sterilization of its parts. The simple organization of the 

 Psilotaceae is, of course, susceptible of the same interpretation — but this has 

 not been the one followed in the above remarks. 



Literature cited. 



1. Bower, F. 0., The Origin of a Land Flora. Macmillan and Co., London, 1908. 



2. Campbell, D. H., The Eusporangialae : the Comparative Morphology of the 



Ophioglossaceac and Marattiaceae. Carnegie Institution, Washington, 1911. 



3. Darnell-Smith, G. P., The Gametophyte of Psilotum, Trans. Roy. Soc. Edin., 



vol. 52, pt. i, pp. 79-91, 1917. 



4. Holloway, J. E., Studies in the New Zealand Species of the Genus Lycopodium, 



Part I, Trans. N.Z. Inst., vol. 48, pp. 255-303, 1910. 



5. Ibid., Part II, Methods of Vegetative Propagation, Trans. N.Z. hist., vol. 49, 



pp. 80-93, 1917. 



6. Ibid., Part III, The Plasticity of the Species, Trans. N.Z. Inst., vol. 51, 



pp. 161-216, 1919. 



7. — ■ — ■ The Prothallus and Young Plant of Tmesipteris, Trans. N.Z. Inst., vol. 50, 



pp. 1-44, 1918. 



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



from the Rhynie Chert Bed, Aberdeenshire : Part I, Rhynia Gwynne- 

 Vaughani, Trans. Roy. Soc. Edin., vol. 51, pt. iii, pp. 761-83, 1917. 



9. — • — ■ Ibid., Part II, Additional Notes on Rhynia Civynne-Vavghani, with Descrip- 



tions of Rhynia major and Hornea Lignieri, Trans. Roy. Soc. Edin., vol. 52, 

 pt. iii, pp. 603-27, 1920. 



10. ■ Ibid., Part III, Asteroxylon Mackiei, Trans. Roy. Soc. Edin., vol. 52, pt. iii, 



pp. 643-80, 1920. 



11. Lawson, A. A., The Prothallus of Tmesipteris tannensis, Trans. Roy. Soc. Edin., 



vol. 51, pt. iii, pp. 785-94, 1917. 



12. ■ The Gametophyte Generation of the Psilotaceae, Trans. Roy. Soc. Edin., 



vol. 52, pt. i, pp. 93-113, 1917. 



13. Osborn, T. G. B., Some Observations on the Tuber of Phylloglossum, Ann. Bot., 



vol. 33, pp. 485-516, 1919. 



14. Solms Laubach, Der Aufbau des Stockes von Psilotum triquetrum und dessen 



Entwickelung aus der Brutknospen, Ann. du jard. bot. de Buit, vol. 4, 

 pp. 139-94, 1884. 



15. Thomas, A. P. W., The Affinitv of Tmesipteris with the Sphenophyllales, Proc. 



Roy. Soc, vol. 69, pp. 343-50, 1902. 



