Pteridophytes . Are they vestigial? 263 
and have not touched the broader and more contentious ques- 
tion of the relations of the vegetative and reproductive parts. 
On the other hand, as Goebel has pointed out, all incom- 
pletely developed parts are not to be assumed to represent 
parts which have been functional in the ancestry; and in dealing 
with the Pteridophytes, as also with Flowering Plants, we must 
distinguish between those parts which are really arrested and 
vestigial, and those which are simply supernumerary primordia. 
It is on a basis of comparison, combined with examination of 
the individual part, that this distinction can be drawn : such 
comparison in the large living genus, Lycopodium , has led to 
the view that the arrested sporangia at the base of a strobilus 
are really vestigial, while those at the apex may be simply 
supernumerary. 
Perhaps for our present purpose the best analogy with this 
is to be found in Prantl’s theory of the honey-leaves in the 
Ranunculaceae h Prantl showed that the glandular honey- 
leaves are, on the grounds of form, position, and development, 
to be taken as stamens, which in place of forming pollen-sacs, 
developed usually as honey-secreting structures : they are in 
fact sterilized sporophylls. Their appearing prior to the 
stamens in the ontogeny does not prevent the floral morpho- 
logist from admitting their derivation by metamorphosis from 
stamens, which in their fully developed state are formed 
later in the individual flower. We may leave on one side for 
the present the wider question raised by Drude 2 whether 
other parts of the flower also may not be metamorphosed 
stamens : on Prantl’s theory of the honey-leaves an analogy is 
provided for us, which fits the present view for the sporophylls 
and sterile foliage leaves of Lycopodium : in both cases it is 
suggested that, by functional and structural modification, 
a series of parts differing in function from the original type 
has been intercalated: and that though these appear earlier 
in the individual, they were of later origin in the descent. It 
is thus attempted in this paper to apply to the strobiloid 
Pteridophyta the same method as is accepted in the morpho- 
1 Engler’s Jahrb., vol. ix, p. 225. 8 Schenk, Handbuch, iii, 2, p. 302. 
