1054 
Benson.—New Observations on 
There is no vestige of a stellate character in the transverse section of 
the stem stele of either genus. The smaller internal elements do not 
contribute to the trace in either. In Botryopteris there are far fewer 
mesarch groups of protoxylem ; hence the giving off of a leaf-trace approxi¬ 
mates very closely to a simple dichotomy, and resembles what one would 
expect to find in a primitive Pteridophyte. 
We cannot but regard Botryopteris as having a close affinity with the 
Zygopterideae, in spite of the outstanding contrast in the mode of branching 
of their petioles. The presence of aphlebiae, now for the first time recorded 
in a species of Botryopteris , is a new feature of resemblance. If the 
Botryopteris type does not owe its simplicity to reduction, then the 
Zygopterid type must owe its complexity to elaboration. 
The fundamental difference may possibly be traced back to the origin 
of the Zygopterid leaf-trace, from parts which in their ancestors gave rise to 
more than one trace, but we must wait for more facts before the problem 
of the common origin of the mono- and bisymmetric type of petiole can 
be solved. That the more complex type is the derived type is suggested 
by the ontogeny ; the gradual series of changes which occur in a single 
petiole of Metaclepsydropsis or Diplolabis (so beautifully represented in 
Dr. Gordon’s figures *) as it passes from the nodal form to the upper part 
of the main rachis may possibly be regarded as representing in some degree 
the phases in its evolutionary sequence. 
X. Summary. 
A considerable amount of new material of the Pettycur species of 
Botryopteris having become available, it has been possible to give details 
of its structure, especially with regard to its stelar anatomy and the presence 
of aphlebiae at the base of its smaller leaves. 
Botryopteris antiqua , Kidston, is a form which, though variable, is 
often as large and well differentiated as Botryopteris ramosa. The proto¬ 
xylem elements of the leaf-trace before it leaves the axis are mesarch, 
and later are aggregated into either one or two adaxial grooves, and are 
not evenly distributed. Heterophylly obtained, for those petioles which 
are supplied by a monarch trace are found to possess a uninerved sheathing 
organ which is regarded as of the nature of an aphlebia. The diarch petioles 
show no trace of this organ. 
The axis was of the nature of a rhizome which at intervals gave off 
numerous adventitious roots. 
The xylem of the stem stele is differentiated differently in the leaf¬ 
bearing part and the root-bearing part. The distribution of the protoxylem 
has been clearly shown in both types of structure and the departure of 
1 Gordon : loc. cit. 
