Equisetaies. 169 
equal force here, and in this case they receive additional support 
from the extreme antiquity of Archaeocalamites. One might then 
explain the occasional sterile whorls of Pothocites (7) as being the 
first indication known to us of the sterilization of some of the lobes ; 
in Calamostachys and Palccostachya the dorsal lobes of the sporophylls 
are no longer sporangiophores, but have been sterilized. It is fair 
to add, however, that Graf Solms-Laubach considers that the cone 
of Pothocites, which is certainly ill-understood, has been misinterpreted 
(17). This derivation of a completely fertile cone from a type 
resembling Sphenophyllum fertile by the displacement of the upper 
lobe of a dorsiventrally divided sporophyll, of which both lobes 
were fertile, has been suggested by Dr. Scott, who applies the 
suggestion to the Equisetum-type (15) ; the types of Equisetum and 
Archaeocalamites are, however, identical in fundamental structure, 
and what applies to one probably applies to the other also. 
Nevertheless the writer has not been able to find any passage in 
which Dr. Scott affirms, or even suggests a homology between 
alternate whorls of the sporangiophores of Archaeocalamites and the 
sterile bracts of Calamostachys. Indeed if he regards the fertility 
of the dorsal segments of the sporophyll of Sphenophyllum fertile as 
a later modification he could hardly derive so ancient a form as 
Archaeocalamites from this type. Professor Jeffrey takes a somewhat 
different view, for though he suggests a dorsiventral lobing of the 
sporophyll in the ancestors of the Calamariae, he gives two alter¬ 
native ways of accounting for the absence of sterile whorls in cones 
of certain members of the phylum; (a) that the “sporangiophores” 
of completely fertile cones represent fused dorsal and ventral lobes 
and (b) that the sterile dorsal lobes have become obsolete (6). 
There is, as he himself points out, at present no evidence in support 
of either of these views; but since their publication the discovery 
of Sphenophyllum fertile has shown that the dorsal lobes of a sporo¬ 
phyll may be fertile, and as Dr. Jeffrey is seeking to derive the 
Equisetaies from the Sphenophyllales it would seem natural for 
him to accept the explanation given here of the completely fertile 
cones. The writer considers that the occasional sterile whorls 
which are present in Phyllotheca as in Pothocites may possibly be 
sterilized sporangiophores, which, with the loss of their reproductive 
functions, have acquired greater vegetative development. Both 
Potonie (10) and Professor Seward (16) have drawn attention to 
the similarity between an abnormal cone of Equisetum, figured by 
the former, in which sporangiophores occur below a sterile whorl, 
and a fructification of Phyllotheca. Potonie states that this abnor- 
