Sykes . — The Anatomy and Morphology of Tmesipteris. 85 
Lycopodium , and were placed by Baker 1 in the Lycopodiaceae, as genera 
equivalent in value to Lycopodium. Campbell 2 still places the order 
Psilotaceae in the Lycopodiales ; Scott 3 prefers to found a group, Psilotales, 
which is more nearly allied to the Sphenophyllales than to the Lycopodiales; 
Thomas 4 and Bower 5 have come to the conclusion that the Psilotaceae 
are sufficiently nearly allied to the Sphenophyllaceae to warrant a position 
in Sphenophyllales. 
It is, perhaps, well to recapitulate here the resemblance noted by 
Scott and Thomas between the Psilotaceae and Sphenophyllaceae. These 
are — secondary thickening in P silo turn and Sphenophyllum ; mesarch position 
of the protoxylem in Tmesipteids and Cheirostrobus ; and the similar morpho- 
logical nature of the spore-bearing organs in the two families. These authors 
believe that the synangial ‘ branch ’ in Tmesipteris is to be compared with a 
sporophyll of Sphenophyllum or Cheirostrobus , the synangium with its pedicel 
being equivalent to the sporangium or sporangia with the sporangiophore, 
borne by a sporophyll of one of these cones, the leaves of the synangial 
‘ branch’ corresponding to the sterile segments of such a ‘sporophyll They 
think also that the dichotomous division of the sporophylls in the Psilotaceae, 
the fact that their sporophylls are more elaborate than the vegetative leaves, 
the groups of sporangia on a single sporophyll, cases of abnormally branched 
sporophylls, and ‘ the normal modification of the ventral leaf-lobe to 
form the synangium ’, are all indications of affinity with the Sphenophyllales. 
While many of these latter points of comparison are dependent on the 
authors’ interpretation of the morphology of the synangial branch, it has 
been shown above that others may be explained on the axial theory of the 
homology of that organ, and the great similarity between the sporophylls 
of Tmesipteris and Sphenophyllum majus , both in distribution on the axis 
and in general appearance, is alone enough to suggest some relationship 
between the two families. But unless it is possible to look upon the 
sporophyll in Sphenophyllum and Cheirostrobus as a sporangiophore, which 
is axial rather than foliar in nature, bearing both leaves and sporangia, 
such a sporophyll does not seem to me to be comparable with the fertile 
branch of Tmesipteris. 
Lignier 6 has placed the Psilotaceae in a position which implies their 
near relationship to the ‘ Protopteridophyta and supposes that they arose 
from that stock before the first Protofilices, which class gave rise to the 
Filices, Equisetales, and Sphenophyllales, were evolved. He lays stress 
on a connexion between the Psilotaceae and the Lycopodiaceae. 
On the whole the relationship of the Psilotaceae must be acknowledged 
to be still obscure, and for the present it seems best to place them in 
a separate cohort, the Psilotales, as has been suggested by Scott and others. 
1 Baker, 1887, p. 29. 2 Campbell, Mosses and Ferns, 1905, p. 485. 
3 Scott, Studies, 1900. 4 Thomas, 1902. 8 Bower, 1903. 6 Lignier, 1903, p. 95. 
