i 16 A Branched Cone of Equisetum. 
Fig. 20b shews a section of a bundle near its uppermost limit. 
Fig. 20d represents a section of a bundle just before dying out in the 
downward direction. 
At the British Association meeting of 1901, Mr. Gwynne- 
Vaughan 1 shewed that the so-called vascular bundle of Equisetum 
consists of three strands ; a carinal strand, part of which passes 
out as a leaf-trace, and two lateral cauline strands. He also 
found that whereas the xylem of the carinal strand is mostly or 
wholly centrifugal in its development, that of the lateral strands 
shews indications of having been formed centripetally. He came to 
the conclusion that the stele of Equisetum was in all probability 
originally protostelic and that the lateral cauline strands represent 
the remnants of a former large development of centripetal wood. 
The discovery made by Dr. Scott, 2 announced at the same meeting, 
of centripetal wood in the stem of Calamites pettycurensis lent 
support to this view. 
It is perhaps possible, as Professor Seward suggested to me, 
that the bundles in the pith of the branched cone of Equisetum 
may be the remnants of the solid central stele of the ancestors of 
the living species of Equisetum. Since these bundles are quite 
unconnected with the normal ring of vascular tissue they are 
evidently not formed by the branching of normal strands, More¬ 
over, their structure is different from that of the normal bundle, 
their resemblance being rather to a simple protostele than to 
anything else. 
Having regard to these two facts, together with the probable 
absence of phloem from the medullary vascular strands, and 
bearing in mind that it is in the reproductive parts of plants that 
pre-existing structures are likely to occur, it would seem quite 
possible that the medullary strands in question are the remains of 
a primitive solid central mass of centripetal xylem. 
1 Gwynne-Vaughan. Brit. Ass. Rep., 1901 ; Annals of Botany, 
Vol. XV., p 774, 1901. See also Bower, Origin of a Land 
Flora, p. 388, 1908. 
2 Scott. Brit. Ass. Rep , 1901 ; Annals of Botany, Vol. XV,, p. 
773, 1901. 
