Cone of Equisetum maximum , Lam. 603 
the sporangiophoric traces, anomalies which are found especially frequently 
in E. maximum , indicate a certain reduction of the protoxylem system. It 
is not possible in the present publication to deal at all fully with the course 
of the strands of protoxylem in the axis. It may, however, be stated that 
a study of the course of this system reveals the occasional existence of 
protoxylem strands unconnected with the main axial system of protoxylem. 
Two such detached strands have already been recorded from the cone of 
E. sylvaticum (Browne, 1921, p. 454). Such cases can hardly have arisen 
except by the poor development of the protoxylem system. Below the in¬ 
sertion of the lowest whorls both of Cones A and F of E. maximum one of 
the protoxylem strands supplying a normal trace was found to terminate 
blindly 300-500 /i lower down. Possibly a detailed study of Cones A and 
B would yield other examples of protoxylem strands ending blindly in 
a downward direction, though no others were found in Cone F. In the 
lower region of Cone G—the only part studied—there were five axial strands 
of protoxylem with blind basal endings. In two cases strands of protoxylem 
which appear, as we pass upwards, to arise de novo in the metaxylem are so 
clearly in the line of continuation of the protoxylem that died out 300-500 n 
lower down that it is difficult not to regard them as separated from the main 
system by a local failure of certain cells to develop as tracheides. In neither 
of these cases did the main protoxylem strand pass out as a trace at the 
level of the next whorl of sporangiophores. On the contrary, these proto¬ 
xylem strands were still pursuing their upward course when the series of 
sections came to an end and both had given off traces to members of several 
whorls. In another case a strand of this sort, which also persisted upwards 
beyond the end of the series of sections, passed through the level of two 
whorls before giving off a trace. Below the lowest whorl of this cone is 
a free strand of protoxylem, about 300 p long. The position of this strand 
is such that it has the appearance of being the continuation of one of the 
branches arising by a supra-annular forking of the protoxylem. The dis¬ 
tance between it and one of these protoxylem branches is about 250 /x. 
These and other cases leave a very strong impression that the free axial 
strands of protoxylem do not represent an increase of protoxylem develop¬ 
ment, but arise rather by local failure of certain stelar cells to develop as 
tracheides. 
Summary. 
1. The occurrence in cones of Equisetum maximum of traces of which 
the protoxylem, though entering the vascular bundle, fails to reach the axial 
protoxylem and dies out in the metaxylem ; of other traces of which the 
phloem only enters into connexion with the corresponding tissues of the 
axis ; and of yet other traces which die out completely in the cortex with- 
