the Anatomy of the Cone and Fertile Stem of Equisetum . 437 
possible to ascertain whether the two strands became confluent, but as they 
were relatively far apart, it is likely that they remained separate, at least for 
some distance (cf. apex of cone in E. arvense , Browne ( 1 ), p. 683). 
In Cones A, C, and D of E. debile the stele near the apex is relatively 
wide, and the traces of the uppermost sporangiophores depart from two more 
or less widely separated vascular strands. In Cone A the two strands, much 
narrowed above the departure of the traces, soon fuse to form the vascular 
supply of the terminal acumen. In Cones c and D the narrower of the two 
axial strands dies out, and the other, after narrowing rapidly above the 
departure of the traces, enters the acumen. In Cone B the traces of the four 
more or less concrescent sporangiophores found at the apex of the cone de- 
part from a closed or rapidly closing ring of xylem, recalling that found in 
a similar position in E. palustre (Browne ( 1 ), p. 683). In Cone E the 
distribution of the phloem indicates that had the differentiation of the meta- 
xylem been complete a similar condition would have prevailed at the apex 
of the cone. 
In Cones A and B of E. variegatum all the vascular strands except one 
pass out in their entirety as traces of the sporangiophores of the uppermost 
whorl. One strand, though giving off a trace of the same size as the 
others, persists and passes into the acumen. After giving off a trace it is at 
first very narrow, but it rapidly widens again and remains for some time 
markedly wider than were the strands a little lower down. In Cone C the 
structure of the apex is somewhat different. The tracheides of the vascular 
strands of the acumen, though they approach very close to one of the 
vascular strands of the axis, do not actually come into contact with any of 
them. All the bundles of the axis pass out as traces, except one, which, 
though giving off a trace similar to the other traces, persists as a very 
narrow strand. This narrow strand approaches the main vascular supply 
of the acumen, but does not fuse with it, and dies out before it. The struc- 
ture of the apex in this specimen appears to be slightly anomalous. It 
seems likely that the want of continuity between the tracheides of the 
acumen and those of the axial strand they approach is due to an accidental 
and purely local failure of a few cells to develop as tracheides. 
V. The Sporangiophores and their Vascular Supply. 
The stalks of the sporangiophores of E. sylvaticum are relatively long 
and slender, and, excluding the partially concrescent members of the upper- 
most whorl, concrescent sporangiophores are rare, probably because, owing 
to the slenderness of their stalks, they are not so liable to be disposed 
in close proximity to one another. In Cone B, however, the first and 
second and the tenth and eleventh sporangiophores of the eighth whorl are 
respectively basally concrescent in pairs. It is possible that the occurrence 
in a single whorl of two pairs of basally concrescent sporangiophores should 
