67 
Inter-relationships of the Phyla. 
the latter have been, and still are, the subject of much discussion. 
Numerous theories as to the structure of these plants and their 
affinities, varying more or less in detail, have been put forward; 
these may he divided into three groups: (a), Professor Lignier’s 
view that the Psilotaceae are related to the Lycopods and are quite 
distinct from the Sphenophyllales; this botanist regards the 
synangium and its stalk as a cauline structure hearing two phylloids 
or scales homologous with the leaves of the Lycopods, hut not with 
those of other Pteridophyta; ( b ), that of older botanists, such as 
Goebel and Strasburger, who regard the synangium as terminal on 
an axis bearing two fused leaves; this view has been re-stated 
quite recently in a slightly different form by Miss Sykes (39) ; ( c ), the 
synangium is also regarded as a leaf-borne organ, a view held with 
various modifications by Graf. Solms Laubach (37), Professor 
Bower (5), Mr. Vaughan-Jennings and Miss Hall (22), M. Dangeard 
(14), Dr. Scott (34) and Professor Thomas (42). 
Anatomically the Psilotaceae agree fairly well both with the 
Lycopods and the Sphenophyllales, but as already pointed out 
Professor Lignier’s distinction between the phylloids of Lycopods 
and Psilotaceae and true leaves falls to the ground if his own 
criterion of the constantly unifascicular nature of the phylloid is 
applied to the Lycopods. Further the Psilotaceae are, as Dr. Scott 
points out, too obviously reduced to be regarded as perpetuating the 
characters of a series forms in which the true leaf, found in the 
oldest known Ferns and Horsetails had not yet been evolved. This 
view also neglects the similarity of the Psilotaceae to the 
Sphenophyllales made clear by Dr. Scott (34) and Professor Thomas 
(42). The former has pointed out that the position of the 
sporangiferous pedicle on the ventral surface of a leaf or sporophyll 
is closely similar to that of the sporangiophore in the fossil phylum. 
Further the trace that enters the supposed sporophyll divides into 
three bundles of which the median one enters the pedicel of the 
synangium while the two others enter the forks of the sporophyll. 
Thus the relation of the vascular supply of the pedicel of the 
synangium to the trace is essentially that of the sporangiophore to 
the sporophyll in such a form as Sphenophyllum Daivsoni or Cheiro- 
strobus though there are necessarily differences in detail owing to 
the different numerical proportions obtaining between the sporangio- 
phores and the subtending sterile lobes. This relationship and the 
compound sporophyll are very different from anything known in the 
Lycopod fructifications. The abnormalities recorded in considerable 
