SPORE-PRODUCING MEMBERS 383 
accepted that the ovule, like other sporangia, is an organ sw? generis, and 
not the result of modification of a leaf or leaf-segment. The occasional 
existence of sporangia, or even of imperfect sporangiophores upon the 
annulus, is not necessarily a proof of evolutionary transition from the one 
structure to the other, but is rather to be held as indicating that the 
primordium in its ontogenetic origin was not defined in its character. 
The strength of the view stated by Goebel lies in the fact that it is 
supported by all three lines of argument above noted, and if it were 
not for the fossils, which he does not introduce into his discussion of 
the matter, it would probably not be called in question. But comparison 
with them suggests an alternative view, viz. that the sporangiophores are 
not of the nature of phyllomes, but are comparable rather with the 
sporangiophores of the Psilotaceae or Sphenophylleae; these they certainly 
resemble in form and function, though they differ from most of them in 
maintaining no strict relation of position to the true leaves. This sug- 
gestion must now be examined. 
It is based primarily upon those Calamarian strobili in which each 
leaf-whorl is regularly succeeded by a whorl of sporangiophores. In the 
strobili the leaves of successive whorls show a radial alternation, as in 
the vegetative shoot, and it seems natural to suppose that they accordingly 
correspond to the ordinary succession of them in the vegetative region. 
But in addition to the sterile leaves the sporangiophores are present, and 
their presence does not disturb the alternate succession of the leaves. If 
the sporangiophores were rightly regarded as leaves, it might be anticipated 
that the alternate succession of the sterile leaves would be disturbed where 
the sporangiophores intervene between their whorls, but it is not. Again, 
though the number of the sporangiophores is frequently half that of the 
sterile leaves, that numerical relation is not strictly maintained, while their 
disposition in vertical, non-alternating series is on a plan apart from that 
of the alternating whorls of sterile leaves. Their position on the internode 
also, sometimes at the base, sometimes at the upper limit, often in the 
middle, again shows their independence of the sterile leaves. These facts 
together point to their being structures of a different nature from the 
leaves of the strobilus. 
It may be asked how this non-phyllome theory of the sporangiophores 
is compatible with the facts in Zgwzsefum, in which the annulus has 
usually been accepted as a transition from the foliage-whorls to the 
sporangiophores. It is true the annulus lies at the boundary between the 
sterile and fertile regions, and that in Zgu¢se¢wm no vestiges of leaf-whorls 
are found higher up among the sporangiophores. Goebel has pointed out 
an obvious protective use for the annulus, which would sufficiently account 
for its constancy and limited size in the genus.!_ A comparison of other 
types of Equisetineous strobili affords the following explanation of the 
Equisetum strobilus in terms of the fossils. In the genus Archacocalamites 
1 Organography, p. 681. 
