The Phytogeny of the Pteridophyta. 51 
Reinke, J. Botanisch geologische Streifziige an den Kiisten des Herzogtums 
Schleswig. Kiel, 1903. 
Seelheim. Die Durchlassigkeit des Bodens fur Wasser. Forsch. a. d. Geb. 
d, Agrik.-Physik, Bd. 3, 1880. 
Whitney, Milton. Some physical properties of soils in their relation to 
moisture and crop distribution. Bull. 4, U.S. Weather 
Bureau, 1892. 
,, Some interesting soil problems. Year-book, U.S. Dept. 
Agric., 1897. 
Whitney, Milton and Hosmer, Ralph S. Soil moisture. Bull. 9, Div. Soils, 
U.S. Dept. Agric., 1897. 
Wiley, H. W. Principles and practice of agricultural analysis. New York, 
1895. 
THE PHYLOGENY AND INTER-RELATIONSHIPS OP 
THE PTERIDOPHYTA. 
By Lady Isabel Browne. 
VII.—THE INTER-RELATIONSHIPS OF THE PHYLA. 
In discussing the affinities of the phyla it will he convenient to 
consider first the affinities of the Lycopod and then of the Fern 
phylum to the rest of the Pteridophytes, since these two phyla are 
curiously isolated. It is, as Mr. Tansley has recently pointed out, very 
difficult to suppose that any of the phyla originated independently 
of the others from widely separated ancestors, for in that case the 
roots and vascular tissues (including sieve-tubes and xylem) of such 
a phylum would not be homologous with the essentially similar 
structures of other Vascular Cryptogams (40). Nevertheless, Dr. 
Campbell regards the Lycopod prothallus as having originated 
independently of that of the Ferns and Horsetails from a very 
different type (12). The essential similarity of the gametangia 
throughout the Pteridophyta renders this very unlikely. The radial 
symmetry of the Lycopod prothallus certainly affords a striking 
contrast to the dorsiventral symmetry of the gametophyte of the 
Filicales and Equisetales. The prothallus of the Club Mosses has 
been compared to the radially symmetrical gametophyte of the 
