Notes . 
62 1 
ment of a dorsiventral structure, may be held to account for the 
origin of even the most complex forms. 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 acquisition. 
A comparison is drawn as regards position, physiological and 
evolutionary, in the sporophyte, between the fertile zone in certain 
Bryophytes 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 Bryophytes that region is regarded as a residuum from 
progressive sterilization ; it is suggested that the same is the case for 
a strobiloid Pteridophyte, such as Lycopodium. The theory of the 
strobilus, based on this comparison, is that similar causes would lead 
to the decentralization of the fertile tissue in the primitive Pterido- 
phytes 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, characterized 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 
extended sense to include not only the spore-producing organs of 
Psilotaceae, Sphenophylleae, Ophioglossaceae, and 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 
