40 Lang.—Studies in the Morphology and 
apex downwards, it appears that the cylindrical stele in Helminthostachys 
arises in precisely the same way as that of Botrychium , viz. by the union 
of the leaf-traces. The appearance of procambium upon the ventral side of 
the stele, which in longitudinal section appears to be derived directly from 
the stem apex, can thus be explained by the ventral extension of the broad 
leaf-traces, which meet on the lower side of the stem as well as above, and 
the cylindrical stele is thus developed. It is not impossible that the root- 
traces may also contribute to some extent to the development of this ventral 
portion of the stele. 5 
If the last sentence is taken to mean that a ventral portion of the stele 
not derived from leaf-traces is always present, this view would not differ 
so fundamentally from the segmental analysis of the rhizome and stele 
indicated above, though the ? idea of root-traces c contributing 5 to the stele 
is even less satisfactory than that of entering leaf-traces. 1 It is clear, how¬ 
ever, from the context, from the description of particular plants, and from 
the view of the nature of the pith expressed in the first quotation above, 
that Campbell recognizes steles of young plants as resulting entirely from 
the union of successively older leaf-traces. This view leads him to interpret 
certain structural appearances in a way that I am unable to accept. 
Thus, if the description of a young plant given on pp. 71-3 of ‘ The 
Eusporangiatae 5 and illustrated by Figs. 49 and 50 be referred to, it will be 
found that the anatomical relations of the leaves and stems are followed 
from above downwards. The bundle from the youngest leaf is traced 
inwards from above the level of the stem apex to a plane below this. Not 
even a meristematic or procambial equivalent of the stem stele is recognized 
as present below the apex for the trace to join on to, but this leaf-trace 
is regarded as forming the whole of the stele present in the rhizome below 
the apex. On to this the trace of the next older leaf is followed, so that 
the stele below is regarded as made up by the union of the first and 
second leaf-traces, no stem portion other than this being recognized. The 
double nature of the xylem in this stele below the entry of the second trace 
is figured in detail (Fig. 50), and explained as being due to the portions of 
xylem derived respectively from the two leaf-traces. 
The difficulties which have led to this interpretation of the facts seem 
to be due partly to the extreme closeness of the apex to the youngest 
developing leaf, and partly to the fact that the actual apex is sunken and 
ventrally displaced. Thus the leaf-trace is met with above the level of the 
apex, and below this level may be lignified, while the cauline component 
of the stele is still procambial. The double nature of the xylem of the 
stele behind the junction of a leaf-trace is readily seen, and is accurately 
figured by Campbell, but the lower of the two components is not traceable 
to the next younger leaf, but, as shown above, is the ventral and cauline 
1 Roots and leaves might both be regarded as influencing the differentiation of the stele. 
