io8 
Lady Isabel Browne. 
ventral lobes or sporangiophores ; but the course of the vascular 
strands as traced by Mr. Hickling forbids this assumption, for 
though their vascular strands originate at the same point as those 
of the bracts, they first ascend half-way up the internode and are 
then reflexed and follow a downward course, finally entering the 
sporangiophores just above their own point of origin (5). This 
behaviour seems to show that the approximation of the fertile and 
sterile whorls in Palceostachya is secondary and that this type of 
cone arose from a type in which as in Calamostachys fertile and 
sterile whorls were equi-distant from one another; indeed Mr. 
Hickling shows that the traces of the sporangiophores are slightly 
reflexed in a species of Calamostachys, described by Renault as 
Calamodendrostachys Zeilleri (5). It might at first sight appear as 
if Miss Sykes were correct in regarding the position of the 
sporangiophores on the axis as primitive, and in looking upon their 
frequent approximation to the bracts as secondary, since the 
sporangiophores are borne on the axis in Archaeocalamites, Pothocites 
and Calamostachys, and since their approximation to the bracts has 
been shown to be secondary in Palceostachya. It might also be 
used by Professor Bower to support his theory of the independence 
of, and the absence of homology between, bracts and sporangiophores 
(1). But both these writers, in common with the majority of 
recent botanists, admit the affinity of the Equisetales with the 
Sphenophyllales, and on neither of their theories can a satisfactory 
explanation be given of the structure of Sphenophyllum fertile. It 
is therefore preferable to regard the position of the sporangiophores 
on the axis, and their apparent independence of the bracts, as due 
to their displacement; this is strongly supported by the origin of 
the bract- and sporangiophore-trace at the same point on the 
cauline stele, and by the fact that shifting of the sporangiophore 
may clearly occur, since it has occurred in Palceostachya ; this view 
is further borne out by the fact that, as Dr. Scott points out, 
characteristic nodal structure is confined to the insertion of the 
bracts. As regards Archaeocalamites we can hardly escape the 
conviction that its sporangiophores are the homologues of those of 
Calamostachys ; and if so they are not phylogenetically speaking 
entire sporophylls, but lobes of sporophylls that have been separated 
from one another over the internode. In this case both dorsal and 
ventral lobes are fertile and this is probably a primitive character < 
It might of course be said that in Archaeocalamites the sterile bracts 
had become fertile ; but the same very strong objections to this 
view explained in the case of Sphenophyllum fertile apply with 
