38 Lang .— Studies in the Morphology and 
Helminthostachys , are paralleled by the independently evolved shoots 
of the sexual generation of Mosses and leafy Liverworts respectively. 
In the case of the Bryophyta we know that the construction of the mature 
shoot is directly related to the apical segmentation. To what extent such 
a relation holds in the case of the more massive shoots of Ferns is, in my 
opinion, an open question which requires fuller investigation. The view 
has been expressed on the one hand that the leaf-development in Ferns 
is independent of the apical segmentation. 1 On the other hand, we know 
that in certain cases/such as Cercitopteris , the relation between apical 
segment and leaf holds, and this is also stated to be the case for the 
dorsiventral rhizome of Polypodium vulgare . 2 The appearance of the 
mature regions of both radial and dorsiventral shoots is at least consistent 
with assuming such a relation to hold, and is otherwise insufficiently ex¬ 
plained. If such a segmental relation holds for Helminthostachys , for example, 
it would explain the regular succession of the lateral members in a way 
that does not involve the acceptance of any view that denies the existence 
of an axis. On such lines we should be prepared to find that the stele of 
the rhizome could be regarded, in part at least, as cauline, though influenced 
profoundly by the leaves. 
The segmental construction with two rows of dorso-lateral and one 
row of ventral segments is indicated, not only in the general morphology 
of the rhizome of Helminthostachys , but also in the stelar structure. It is 
shown most clearly in smaller rhizomes, where the whole of each dorso¬ 
lateral segment of the outer xylem of the stele is continuous with the 
outgoing leaf-trace. Since the segmental construction is of the rhizome 
as a whole, the vascular system being developed along certain tracts 
through this, only two of the segments may be evident in the stele itself, 
the third being indicated by the departing leaf-trace. In the less extended 
adult type of stele all three segments are represented in any one section. 
Thus the three components of the stele are represented in a large 
rhizome, such as that in Text-fig. 1, B, by the ventral portion where the roots 
are borne, the right dorso-lateral portion concerned with the vestigial bud, 
and the left dorso-lateral portion concerned with the next leaf. In small 
steles the distinction of three parts is shown in Photo 32, where the ventral 
portion and the right dorso-lateral portion are evident in the stele of the 
stem, while the left dorso-lateral segment is represented by the departing 
leaf-trace. The same thing is shown in Photo 52, where the dorso-lateral 
segments are indicated by the leaf-trace (/./.), and by the region with the 
protoxylem group (pxi) of the next trace already evident. The rest of the 
stele corresponds to the ventral segment. 
If the stele be traced into the meristematic region behind the apex, 
1 Cf. the discussion of this question in the Land Flora, pp. 175-7. 
2 Klein : Bot. Zeit., 1884, p. 646. 
