66 Lady Isabel Browne. 
probability that in the primitive members of both phyla the sporo- 
phylls were divided into dorsal and ventral lobes, the lobes being 
sometimes divided laterally into segments. In both this dorsi- 
ventral division of the sporophyll seems frequently to have been 
obscured by the separation of the lobes and by the sterilization of 
the dorsal ones. It is true that since Mr. Hickling’s researches 
Palceostachya can no longer be regarded as a link between the 
Sphenophyllales and Calamostachys, but, as Dr. Scott says, “ the 
evidence of Calamostachys itself is sufficient to establish a clear 
relation between the Calamarian fructifications and those of the 
Sphenophyllales ” (34). The Devonian Pseudobornia may probably 
be another link, for its whorled sporophylls resembling reduced 
leaves suggest comparison with the Sphenophyllales, its probable 
heterospory rather recalls the Equisetales, while in the super¬ 
position of its large compound leaves it resembles both Archceo- 
catamites and many Sphenophyllales. In their protostely and in the 
constant superposition of their leaves the latter phylum seems to 
be the more primitive, while the writer believes that the sporophylls 
of Sphenophyllum fertile are more primitive than those of any 
Equisetales. Nevertheless, Dr. Campbell, in recognizing the 
affinity of the two phyla, remarks that according to the geological 
record “ . . . the solid stele of Sphenophyllum is a more recent 
development than the separated vascular strands of the typical 
Equisetales, as exemplified by Archceocalaniites" (13). If the 
hypothesis of the primitiveness of the protostele rested only on its 
occurrence in the Sphenophyllales it would be weak indeed. 
Actually, however, this assumption is based on the prevalence of 
protostely in the simpler members of all the phyla except the 
Equisetales, on the traces afforded by Protocalamites pettycurensis of 
a derivation of this phylum, also-from forms with solid steles, and 
on the greater proportion of protostelic vascular plants in the 
Palaeozoic rocks than at the present day. It is perhaps strange 
that Dr. Campbell should attach so much importance to the absence 
of undoubted species of Sphenophyllum from the Devonian and 
older formations, for he advocates the view that the Ophioglossaceae 
are the most primitive Pteridophyta, and however weak the 
geological record of the Sphenophyllales, it appears to be over¬ 
whelmingly strong compared to that of the Ophioglossacese. 
This view of the relative primitiveness of the Sphenophyllales 
is borne out by the fact that they form a link connecting such 
different groups as the Equisetales and Psilotales. The affinities of 
