4 Chrysler.—The Nature of the Fertile Spike in 
(Fig. 8), these points break off (Figs. 9, 10) and the two small bundles 
so formed join the main strands on their inner face at a slightly higher level 
(Fig. 11), then the adaxial portions of the main strands break off (Fig. 12) 
and supply leaflets or pinnae on each side. Here of course the branching 
strands do not approximate, but diverge as they pass out to pinnae. The 
same process is gone through in connexion with the exit of the traces 
of the next pair of pinnae. The identity of the mode of origin of the 
vascular supply of the fertile spike and that of a pair of pinnae of the leaf 
indicates, unless there is evidence to the contrary, that the fertile spike 
represents two fused basal pinnae of a leaf, thus supporting the theory 
proposed by Roeper ( 22 ). But it is necessary to show that the mode 
of origin so described corresponds to the mode exhibited in other organs 
admitted to be leaves. 
If the figures just referred to are attentively examined it will be seen 
that each of the strands which supply the fertile spike and the pinnae arises 
from a gap in the curved leaf-trace. This appearance is obscured by the 
fact that the branch strand arises from the side instead of the base of 
the gap, which closes just as the strand makes its exit ; or in other words 
the branch strand adheres to one side of the gap for practically the whole 
length of the gap. That this interpretation of the appearance is the correct 
one is borne out by the observation of Bertrand and Cornaille (2) that 
in the basal part of the petiole there are fourteen £ divergents ’ which run 
more or less united edge to edge ; four of these, that is, two on each side, 
supply the fertile spike. In view of the upright position of the spike 
it is not to be expected that the divergents which supply it will at once turn 
outward, as occurs for instance in an ordinary fern leaf, but they maintain 
their original direction for some distance, thus altering and obscuring 
the gap. It is not necessary to seek far among the large-leaved pterido- 
phytes for petiolar traces with gaps. Fig. 17 shows a transverse section 
through the midrib of Todea barbara at the level where two leaflets arise. 
It will be seen that the vascular supply of a leaflet leaves a wide gap at its 
exit from the curved leaf-trace. In the related genus Osmunda the same 
may be seen, but in this genus the gap is sometimes so narrow that a section 
taken just above the point of origin of the traces of pinnae shows no gap. 
This is represented in Fig. 18, near which (Fig. 19) has been placed a photo¬ 
graph of the corresponding region in Botrychmm virgmianum ; the simi¬ 
larity is too marked to be overlooked. Sinnott ( 23 ) has recently shown 
that this feature is of general occurrence in the Osmundaceae. In Polypo- 
diaceae the leaf-trace has the same general shape, and the gaps left by the 
departure of the vascular strands of the pinnae are generally so narrow that 
no fundamental tissue is to be seen in them, but it can easily be made out 
that these strands do not break off from the free edges of the petiolar trace, 
but are pinched off from the projecting corners of the trace. Only in com- 
