H. Hamshaw Thomas. 
258 
bracts and sporangiophores and their relative arrangement is an 
objection, for while the sporangiophores of successive whorls appear 
to be always superposed, the bracts of successive whorls alternate. 
Jeffrey 1 supposes a bifurcation of each bract to account for the 
usual case where the number of bracts is double that of the 
sporangiophores. The presence of the same number of segments 
in the leaf-whorls below the cone is perhaps an objection to this 
theory. On the other hand, Lignier 3 thinks the sporangiophores 
are of a double nature and represent two fused together. To both 
of these views, Bower 3 objects that the arrangement of the sterile 
and fertile whorls shows that they really have no relation to each 
other. When their arrangement is plotted on a plane surface this 
seems a real objection, but if a diagram is drawn, in which the 
successive whorls are represented as concentric circles, and a ground 
plan is obtained, the results are interesting. Assuming that each 
of the sporangiophores arises midway between the two bracts below 
it, it will be seen that very little shifting is needed to bring the 
former into their present position from what might have been an 
original alternating one. It is therefore scarcely safe, at present, 
to discard entirely the suggested connection between bracts and 
sporangiophores. 
The presence in my cone of the whorl which I have called the 
“ annulus ” may be of some importance, but its structure is not yet 
sufficiently known to permit of any theory concerning it. It was 
probably considerably larger in the earlier stages of the cone, and 
may have primarily had some protective functions. Though its 
base appears leaf-like, yet its presence does not seem to disturb the 
alternation of the whorls above and below. It may possibly thus 
be homologous with the sporangiophores. 
At the present time, I think that the evidence derived from the 
Equisetales is not conclusive in favour of any of the theories yet 
advanced as to the nature of the sporangiophores. Whatever may 
be the theory adopted, it ought to rest mainly on the data supplied 
by this group alone. Evidence supplied by other groups may be 
useful to confirm the conclusions reached, but it is scarcely safe, at 
present, to argue directly from species of one group to those of 
another. 
1 Jeffrey (99), p. 184—5. 
2 Lignier (03). 
3 Bower (08), p. 383. 
