1903.] Morphology of Spore-prod wing Members. 



261 



the decentralisation of the fertile tissue in the primitive Pteridopli3'tes 

 as in the Bryophytes, 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 projecting sporangia, and that they were associated 

 regularly with outgrowths, perhaps of correlative vegetative 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 Lyco- 

 podium as a primitive one, characterised by more definite numerical 

 and topographical relation of the sporangia to the sporophylls than in 

 any other type of Pteridophyta. 



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

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

 tended sense to include not only the spore-producing organs of 

 Psilotacese, Sphenophyllea?, Ophioglossacese, 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 j that they are seated at 

 points where in the ancestry spore-production 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, Sphenophyllese, and Ophioglossacea 1 

 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 spor- 

 angiophore are, septation, upgrowth of the placenta with vascular 

 supply into it, and branching, with apical growth also in the Ophio- 

 glossaceaa. But even in the most complex forms the sporangiophore 

 may be regarded as a placental growth, and not the result of transfor- 

 mation of any other member. 



In the case of Helminthostachys the marginal sporangiophores arc 

 regarded as amplifications from the sunken sporangia of the Ophio- 

 glossum type ; in Eguisetum they are regarded as being directly seated 

 on the axis, and having originated there by a similar progression : 

 they would thus be non-foliar. It is pointed out that though a foliar 

 theory would be possible for Eguisetum itself, it is not applicable to 

 the facts known for the fossil Calamariea), which are so naturally 

 related to it. Thus the strobilus of the Equisetinese is of a rather 

 different type from that of the Lycopods, Psilotaceaft, or even the 



