412 Morphologie und Teratologie. 



A summary of evidence of Variation in number of sporangia by any 

 of these methods is then given for the Lycopodinae, Psilotaceae, Spheno- 

 phylleae, Ophioglossaceae , Equisetineae, and Filicineae ; followed in each 

 case by a theoretical discussion of the bearing of that evidence on the 

 morphölogy of the spore producing members. The general result is that 

 all of them, including even the dorsiventral and megaphyllous types, 

 are referable to modifications of a radial stroboloid type; progressive 

 elaboration of spore-producing parts, followed by progressive Sterilisation, 

 and especially by abortion of sporangia in them, of which there is frequent 

 evidence, together with the acquirement of a dorsiventral structure, may 

 be held to account for the origin of even the most complex iorms. But 

 the vegetative organs once formed may also undergo elaboration, and 

 differentiation pari passu with the spore-producing organs, a point which 

 has greatly complicated the problem, especially in the higher forms; all 

 roots are probably of secondary origin; facts of interpolation of additional 

 sporangia, especially in Ferns, and of apogamy and apospory, are also 

 disturbing influences, which have probably been of relatively recent acqui- 

 sition. 



A comparison is drawn as regards position, physiological and 

 evolutionary, in the sporophyte between the fertile zone in certain 

 ßryophytes and the fertile region of certain simple Pteridophytes, e. g., 

 the Lycopods; though no Community of descent is assumed, the relation 

 of the reproductive to the vegetative regions is the same In the ßryo- 

 phytes that region is regarded as a residuum from progressive Sterili- 

 sation; it is suggested that the same is the case for a strobiloid Pterido- 

 phyte, such as Lycopodium. The theory of the strobilus, based on this 

 comparison is that similar causes would lead to the decentralisation 

 of the fertile tissue in the primitive Pteridophytes as in the ßryo- 

 phytes, and result in the formation of a central sterile tract, with an 

 archesporium at its periphery; that such an archesporium, instead of 

 remaining a concrete layer as it is in the larger Musci, became discrete 

 in the Lycopods; that the fertile cell-groups formed the centres of pro- 

 jecting sporangia, and that they were associated regularly with outgrowths, 

 perhaps of correlative origin, which are the sporophylls. 



Whether or not this hypothesis of the origin of a Lycopod strobilus 

 approaches the actual truth, comparison points out the genus Lycopodium 

 asa primitive one, characterised by more definite numerical and topo- 

 graphical relation of the sporangia to the sporophylls than in any other 

 type of Pteriodophyta. 



Then follows, as a consequence of comparison, the enunciation of 

 a theory of the sporangiophore, a word which is here used in an extended 

 sense to include not only the spore-producing organs of Psilotaceae, 

 Sphenophylleae, Ophioglossaceae, Equisetaceae, but also the sori of ferns. 

 The view is upheld that all these are simply placental growths, and not the 

 result of „metamorphosis" of any parts or appendages of prior existence ; 

 that the vascular supply, which is not always present, is not an essential 

 feature; that they are seated at points where in the ancestry spore pro- 

 duction has been proceeding on an advancing scale; hence they do not 

 occupy any fixed and definite position. It seems probable that at least a 

 plurality of sporangia existed on primitive sporangiophores, and that 

 where only one exists that condition has been the result of reduction. 



The above theories are then applied to the several types of Pterido- 

 phyta. The Lycopods, Psilotaceae, Sphenophylleae, and Ophioglossaceae 

 may be arranged as illustrating the increased complexity of the spore- 

 producing parts, and of the subtending sporophylls ; the factors of the 

 advance from the simple sporangium to the more complex sporangiophore are, 

 septation, upgrowth of the placenta with vascular supply into it, and 

 branching, with apical growth also in the Ophioglossaceae. But even in 

 the most complex forms the sporangiophore may be regarded as a pla- 

 cental growth, and not the result of transformation of any other member. 



In the case of Helminthostachys the marginal sporangiophores are 

 regarded as ampüfications from the sunken sporangia of the Ophio- 



