Inter-relationships of the Phyla. 57 
state of our knowledge, in describing the simpler Lycopod cone in 
the terms of the more complex Sphenophyllaceous ones. Thus, 
though it seems almost impossible not to regard the Lycopod 
sporangium as homologous with one or more sporangia of the other 
Lycopsida the homology of the different parts of the sporophyll of 
the Sphenophyllales, Equisetales and Psilotales with those of the 
Lycopodiales remains obscure. Possibly the simple Lycopod 
sporophyll represents a prior stage of evolution to the apparently 
primitively lobed sporophyll of the three other phyla, and the 
subsequent septation of the sporangium into several sporangia and 
the outgrowth of projections bearing them (sporangiophores) may, 
as Professor Bower suggests, have given rise to the sporophyll of 
the Sphenophyllales. The Lycopod sporophyll may, however, have 
been derived from the dorsiventrally lobed type in either of the 
ways mentioned above. 
To sum up the affinities of the Lycopods: the essential 
similarity of the sporophyte leaves little room to doubt that this 
phylum had a common vascular origin with the other Pteridophyta 
and also that it comes nearer to the other Lycopsida than to the Ferns. 
But the Lycopodiales differ from the remaining Lycopsida in the 
structure of their gametophyte, their constant microphylly and the 
simplicity of their sporophylls. There is some evidence that the 
peculiarities of the prothallus are an adaptation to a subterranean 
habit, but little or none as to whether the microphylly and the 
simplicity of the sporophylls are primitive. 
Dr. Scott has said that fossil botany has thrown no clear light 
on the origin of the Ferns or their relation to other Pteridophyta 
(33). But as regards their vegetative organs the Ferns show 
indications of affinity with other phyla. It would seem that, as in 
the Lycopsida, the primitive type of stele in the Filicales was an 
exarch protostele, for, for reasons given in the fifth of these 
articles, the writer cannot agree with Mr. Tansley that the Ferns 
were primitively endarch. The dichotomous frond seems to be 
more primitive than the pinnate (31) and the dichotomous leaves 
of the more primitive Sphenophyllales and Equisetales though 
smaller and whorled, show a distinct resemblance to Fern-fronds. 
In this respect the newly discovered Pseudobornia ursina, from the 
Devonian of Bear Island is perhaps intermediate between the 
Filicales and the other two phyla, for its leaves though relatively 
large and much divided are whorled (35). Unfortunately its 
systematic position is uncertain. 
