Cer atop ter is thalictroides , (L.) 107 
and a neighbouring stele of the latter ; the two apparently 
unite and then almost immediately afterwards separate again 
or re-divide, a stele resulting from this division occupying the 
same place as the original root-stele, and continuing on its 
upward course as before. Very soon, however, a petiole 
leaves the stem containing three vascular strands ; of these 
two are given off from the stem, the third being the one 
which has, lower down in the stem, formed this curious con- 
nexion. 
Fig. 8 represents a diagrammatic longitudinal section of 
a young stem of Ceratopteris , showing this relation between 
these bundles of the petiole, root, and stem respectively. 
In the mature stem no such regular arrangement can be 
made out as has been described in the young plant. The 
roots arise directly from the petioles and have no connexion 
with the stem. No definite behaviour can be made out in 
regard to any of the steles of the stem. The large steles of 
the outer circle are continually uniting and dividing, and at 
certain levels pass out to the leaves, each leaf receiving the 
whole or part of several steles. In tracing a mature petiole 
downwards and into the stem, it is seen that the bundles 
composing the two rings become fewer in number owing to 
the union of adjacent petiolar strands. From these larger 
strands numerous small branches are given off, which form 
a network in the centre of the entering petiole, and finally ’ 
pass inwards to the centre of the stem. These are the small 
inner bundles of the stem which have been already described 
as ending abruptly at varying levels lower down in the stem. 
In other words, the small, inner and feebly developed bundles 
of the stem seem to arise as branches of the large steles of 
the outer ring on the passage of the latter out to a leaf. Since 
in the young plants steles of one size alone are found, 
and these, as in the case of the large outer bundles of the 
mature stem, pass out either as a whole or in part to the 
leaves, the two systems must be regarded as corresponding 
to each other. The large outer bundles may therefore 
be regarded as primitive, the small inner bundles, which 
