260 Browne.—A Second Contribution to our Knowledge of the 
Of course the width of the stele is not the only, nor the principal 
factor causing reduction of the vascular system ; it is, for instance, 
characteristic of E. arvense to have cones containing more axial xylem, 
both actually and relatively to their size, than those of E. palustre , 
though the steles of the former species are usually much wider than 
those of the latter. I am inclined to believe that the relatively large 
amount of xylem at the apices of the cones of E. palustre (Browne, 
p. 6 83) is due to the considerable reduction in width of the stele in this 
region. 
E The downward curvature of the traces of the sporangiophores in 
the lower part of the cone of E. maximum recalls the downward curvature 
of the sporangiophore traces described by Hickling in Palaeostachya vera 
(Hickling, 1 , pp. 375-6). This similarity seems to me no indication of 
a close affinity, for, so far as we can judge, the sporangiophores of Equisetum 
appear to be whole appendages, while those of Palaeostachya seem to 
be morphologically lobes of a fertile leaf. It is worth noting that in 
the larger, very irregular Cone B of E. maximum , in which the whorls were 
often locally duplicated, there was very rarely any indication of any dorsi- 
ventral duplication of any individual trace. Even the analogy is not 
a very close one. In Palaeostachya the traces of the sporangiophores 
ascend steeply upwards through about half the internode, and are then 
sharply reflexed downwards. The angle thus formed between the outer 
and inner parts of the course of the trace is filled by sclerized tissue, and the 
latter also lines the underneath of the trace when, at the extreme periphery 
of its course, it passes out horizontally and enters the sporangiophore. In 
the lower whorls of mature cones of E. inaxiimim it is common for the 
downward course of the trace to be steeper in its outer than in its inner 
part (Text-fig. 1); but except for the course of the trace represented 
diagrammatically in Text-fig. 1. 6, apparently an exceptional course 
affording no good basis for generalization, I have never, in these lower 
whorls, observed traces directed upwards even in the inner part of their 
course. This seems to be due to the fact that in the lower whorls the 
sporangiophores originate as structures at right angles to the axis and 
do not point obliquely upwards. 
Were a reflexed sporangiophore to exert a pull on the trace of a cone 
in which the sclerenchyma was distributed as in Palaeostachya vera> it 
would only affect the sporangiophore trace in the outer part of its course, 
since the buttress of sclerized tissue outside the inner part would be far too 
strong to allow this part of the trace to respond directly to the downward 
pull. But it would seem that no such reflection of sporangiophores can 
account for the downward sweep of the sporangiophore trace of Palaeo¬ 
stachya , for in Hickling’s diagram the sporangiophores are directed obliquely 
upwards, a condition also observable in Fig. 21 of ,his Plate XXXIII, 
