556 Bancroft.—A Contribution to our 
has at its lowest levels a single immersed pole near its anterior margin. 
As the trace passes out, the protoxylem, which either remains single or 
is duplicated, becomes external, its elements lining one or two shallow 
adaxial grooves. Sometimes the protoxylem elements appear to be 
distributed on the anterior margin of the trace. 1 
In the case of R. cylindrica the foliar trace possesses at its lowest 
level a single external pole; a little higher in the trace, the presence of 
a few adaxial metaxylem elements, in some instances, indicates a relic of an 
ancestral structure, such as that realized in B. antiqua. The protoxylem 
is, at still higher levels, more or less external in all cases, its behaviour and 
arrangement in the typical a petioles being very similar to that described 
for B. antiqua . Sometimes, however, when the protoxylem groups appear 
to form two minute points, there is a hint of progression towards the con¬ 
dition seen in the tridentate 2 petioles of Botryopteris ramosa and B. hirsuta . 
In these species, the petiolar vascular bundle is typically triarch, the proto¬ 
xylem elements being aggregated into points of very varying prominence 
in different specimens. The three groups result from the division of the 
single pole of the leaf-trace. 
Miss Benson 3 explains the increase in the number of poles from one 
to three in the evolution of the botryopteridean trace, as being due to the 
arrest of branching at an early stage ; this increase seems to be accompanied 
by the gradual protrusion of the protoxylem groups. 4 In accordance with 
this view, it is suggested that R. cylindrica represents an intermediate, 
though not very advanced, stage in the series, for while protrusion of the 
protoxylem is indicated in some specimens, its arrangement is usually more 
reminiscent of that in B. antiqua . 
According to Paul Bertrand’s earlier work, 5 the botryopteridean trace, 
as represented by that of B. forensis, may be derived from the reduction of 
an ancestral bipolar form. As Scott 6 notes, this author does not take into 
account the trace in related and older types ; while Miss Benson 7 shows 
that if Bertrand’s view be accepted, the early occurrence of a monarch trace, 
in B. antiqua , indicates a process of simplification within the series—an 
indication with which the triarch petiolar bundles of later species are not 
in harmony. It seems more reasonable to regard at least B> antiqua , 
1 Kiclston (’ 08 ), p. 363 ; Pelourde (’ 10 ), p. 365, Fig. 2. 
2 Felix, J. : Untersuchungen iiber den inneren Bau westfalischer Carbonpflanzen. Abhandl. 
Kon. Preuss. geol. Landesanst., Bd. 7, 1886, p. [153]. See p. [164], and Taf. I, Fig. 2. 
Scott (’ 98 ), p. 1050. 
In (3 petioles, the single pole typically forms a distinct point. 
3 1 . c., p. 1051. 4 ibid., Text-fig. 2, p. 1051. 
6 1 . c. (’ 09 ), p. 238. 
6 Scott, D. H. : Review of Dr. P. Bertrand’s work, Etudes sur la fronde des Zygopteridees 
(Lille, 1909). New Phyt., vol. 8, 1909, p. 266. See p. 271. 
7 1 . Ci, p. 1053. See also Bertrand’s general agreement with Miss Benson’s criticism, (T 2 ), 
P- 233. 
