THE 
NEW PflYTOIiOGIST. 
Vol. VII., Nos. 2 & 3 March 31ST, 1908. 
LECTURES ON THE EVOLUTION OF THE 
FILICINEAN VASCULAR SYSTEM. 1 
By A. G. Tansley, M.A. 
University Lecturer in Botany, Cambridge. 
LECTURE X. 
A Comparison of the Vascular System of the Ferns with 
THAT OF OTHER PHYLA OF VASCULAR PLANTS. 
We are undoubtedly justified in concluding that the primitive 
vascular system of the shoot of vascular plants is what has been 
called a protostele, i.e., a solid strand of tracheal-tissue with or 
without intermixed parenchyma, typically circular in transverse 
section, surrounded by phloem and probably also by pericycle and 
endodermis. This conclusion is pointed to, first by the occurrence 
of this type of cylinder (1) among the Lycopods, particularly in the 
earlier Palaeozoic forms, 2 (2) among the Psilotales, (3) in the 
Sphenophyllales, (4) among those Leptosporangiate Ferns which we 
have other reasons for regarding as primitive. Secondly it is 
pointed to by the occurrence of the protostele in the young plants 
of practically all Pteridophytes that have been investigated. Thirdly 
we have the evidence derived from its occurrence in the gametophyte 
of the Mosses (in the form of a simple compact strand of water¬ 
conducting elements which may or may not be surrounded by a 
specialised tissue for conducting soluble organic substances), and in 
the thallus of a few Liverworts. These Bryophytic gametophytes, 
though of course they have no phylogenetic connexion with the 
1 A Course of Advanced Lectures in Botany given for the 
University of London at University College in the Lent 
Term, 1907. 
2 See especially Kidston, On the Internal Structure of Sigillaria 
rItgans of Brongniart’s “ Histoire des vegetaux fossiles.” 
Trans. Roy. Soc., Edin., 41, Part III. (23), 1905, p. 548. 
