﻿288 BOTANICAL GAZETTE [april 



pteridophyte, such as Lycopodium. The theory of the strobilus, based 

 on this comparison, is that similar causes would lead to the decentrali- 

 zation of the fertile tissue in the primitive pteridophytes 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 centers 

 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, characterized by more definite numerical 

 and topographical relation of the sporangia to the sporophylls than m 

 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 m 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-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, Sphenophylleae, and Ophioglos- 

 saceae 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 sup- 

 ply 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 placental growth, and not the result of transformation of 

 any other member. 



In the case of Helminthostachys the marginal sporangiophores are 

 regarded as amplifications from the sunken sporangia of the Ophio- 



