622 
Notes. 
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 Ophio- 
glossaceae 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 com- 
plex 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 sporan- 
giophore 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- 
glossum type ; in Equisetuvi 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 Equisetum itself, it is not applicable to 
the facts known for the fossil Calamarieae, which are so naturally 
related to it. Thus the strobilus of the Equisetineae is of a rather 
different type from that of the Lycopods, Psilotaceae, or even the 
Ophioglossaceae, in all of which there is a constant relation of the 
spore-producing parts to the leaves ; in the Equisetineae no such con- 
stant relation exists ; the leaves and sporangiophores may be in juxta- 
position, as in Calamostachys, without exactly matching numerically; 
or the sporangiophores may occur in larger numbers and in several 
ranks, between successive leaf-sheaths, as in Phyllotheca and Bornia ; 
or without any leaves at all, as in Equisetum . Thus, on a non- 
phyllome theory the latter may be held to be only an extreme case of 
what is seen in certain fossils. 
The Ferns, notwithstanding their apparent divergence of character 
from other Pteridophytes, may also be regarded as strobiloid forms, 
with greatly enlarged leaves; the primitive sori of the Simplices 
resemble the sporangiophores of other Pteridophytes ; the more com- 
plicated soral conditions of the Gradatae and Mixtae were probably 
derivative from these, the chief difference being due to the interpolation 
