W. C. Worsdcll. 
166 
axis, giving thus to each leaf a sort of sole-like expansion to its axial 
insertion, the sporangiophores of Cnlamostachys may, therefore, he 
regarded as still inserted upon the sporophyll, viz : upon the upward 
extension of its basal portion, although they appear to be so entirely 
separated therefrom. It is thus probable that a gradual shifting of 
the sporangiophore from the upper surface of the sporophyll ( Cheiro- 
strohus), first to its axil ( Palceostachya ), and finally entirely on to 
its upper axial foliar base ( Calamostachys ), has taken place. 
In the case of Equisetum and Archceoealamites, where sporangio¬ 
phores only occur on the axis, it seems not at all unreasonable to 
suppose that the sporophylls themselves have become completely 
eliminated (the antiquity of Archceoealamites need not interfere with 
this view), and thereafter the sporangiophores themselves became 
rearranged owing to the requirements of space-economy. Such 
elimination of members, succeeded by a rearrangement of those 
remaining, is seen, I would submit, in the androecium of certain 
flowers, e.g. Tropceolum, where two whorls of five are now represented 
by a single whorl of eight. Hence, in the two above-named genera 
the sporangiophores may be regarded as complete sporophylls in 
themselves. 
In the Lycopod-phylum, which probably also branched off from 
the Sphenophyllales, no great development of the sporangiophore, 
apparently, ever took place. In Spencerites the entire sporophyll 
curiously simulates in shape the sporangiophore of a Calamite, 
inasmuch as it is peltate, yet betrays its distinct origin by bearing a 
single sporangium on the upper lobe only of the leaf. Sigillariostrohus 
Crcpini would appear also to belong to this type. 
In Lepidodendron, Sigillaria, Isoetes , Lycopodium , Selaginella and 
Phylloglossum the sporangium is situated on the upper surface of 
the sporophyll. In some of these cases, as in Lycopodium , a distinct 
sporangiophore or sporangial pedicel is present, although of small 
development. 
Now it is extremely interesting to note that in this phylum of 
plants we find a perfectly parallel case to that existing in the 
Equisetales, as regards the varying position on the sporophyll of the 
sporangium (or sporangiophore). In the fossil genera and Isoetes 
nothing could be more conspicuous than the clearly-defined foliar 
origin and position of these structures. In some species of Lyco¬ 
podium, however, the sporangiophore is in a perfectly axillary posi¬ 
tion, thus exactly corresponding to the case of Palaeostachya in the 
parallel phylum. Now mark the case of Selaginella: here the 
