SPORE-PRODUCING MEMBERS 383 



accepted that the ovule, like otheK sporangia, is an organ si/i 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 

 primofdium 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 

 jrile leaves, that numerical relation is not strictly maintained, while their 

 lisposition in vertical, non-alternating series is on a plan apart from that 

 )f the alternating whorls of sterile leaves. Their position on the internode 

 also, sometimes at the base, sometimes at the upper limit, often in the 

 mkldle, 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 Equisetum, 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 Equisetum 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. 1 A comparison of other 

 types of Equisetineous strobili affords the following explanation of the 

 Equisetum strobilus in terms of the fossils. In the genus Archaeocalamites 



1 Organography, p. 68 1. 



