Knowledge of Rachiopteris cylindrica , Will. 559 
With regard to the foliar trace, the exact details of its emission have 
not been described, but it is evident that the fully-formed petiolar bundle 
is much more complicated than that of the four species just considered. 
It is, in general shape, like an co, the arms of which point towards the centre 
of the stem, and it has been compared with the tridentate bundles of 
B. ramosa and B. hirsuta, where the three projections are much smaller. 
In B. forensis the foliar bundle is described as consisting of an 
essential or ‘ principal 5 segment—the centre arm of the co ; and two 
accessory or * receptive ’ segments—the two lateral arms. 1 These latter are 
believed by Bertrand to be secondary developments to compensate for the 
extreme reduction of the essential part of the trace and to provide the 
metaxylem of'the branch-traces. The principal segment was originally 
considered to have been derived from a primitive bipolar trace, in which 
extreme contraction of the anterior surface had taken place 2 ; more recently 
Bertrand 3 has admitted that the Botryopteridean trace may have been 
derived directly from a unipolar ancestor. In either case, however, its 
reduction was apparently such as to require the development of the recep¬ 
tive parts, and these were, according to Bertrand 4 already present in the 
older types B. antiqua and B. ramosa , although in a condensed state, form¬ 
ing one mass with the principal segment. 
Branching phenomena certainly demonstrate that the centre arm of the 
a) must be regarded as the essential segment. At the base of the petiole, it 
possesses, at its free extremity, two lateral, slightly-sunken poles, 5 which by 
their division provide the protoxylem strands of the branch traces. 
The central arm of the <0 is thus, at this stage, a much more elaborate 
structure than the central point of a tridentate petiolar bundle. Higher in 
the leaf, however, it possesses only a single terminal protoxylem group, and 
according to Bertrand and Cornaille, 0 further reduction of the trace produces 
tridentate bundles, similar to those of B. hirsuta , which, as already men¬ 
tioned, are also held to include principal and receptive segments in a 
condensed state. The ultimate traces of B. forensis are monarch, but these 
cannot be compared with the monarch phase of the earlier species, for 
they are said to consist only of the two receptive segments, the principal 
segment not being represented at this high level; the monarch phase of 
the British species, on the other hand, must include the principal 
segment. 7 
The significance of these facts is doubtful; for if B. forensis , B. ramosa , 
and B. hirsuta belong to the same series, and if the simpler tridendate 
traces are representative of a reduction phase, then the geologically older 
1 Bertrand (’ 09 ), p. 238; Bertrand and Cornaille (’ 10 ), p. 1019; Bertrand (’ 12 ), pp< 230 
and 231. 
2 Bertrand (’ 09 ), p. 238, 3 1 . c. (’ 12 ), p. 233. 4 1 . c. (’ 12 ), p. 232. 
6 Bertrand (’12), p. 231, Big. 26. 6 1 . c., p. 1022. 7 ibid., p. 1022. 
