34 Lang.-^-Studies in the Morphology and 
there was a progressive diminution in thickness, and the stele exhibited 
changes similar to those seen in the ascending series of complexity traced 
in rhizomes of increasing size, but in a converse direction. At the level 
shown in Photo 52 the stele agreed in size and organization with those of 
small branches or young plants in which the scattered elements of inner 
xylem formed, with the cells of the central parenchyma, a mixed pith. 
The stele had returned to the juvenile type, and the changes in relation to 
the departure of a leaf-trace agreed with this. A corresponding, though 
less extreme reduction, is seen on comparing Photos 48 and 50 from 
another piece of rhizome. Both pairs of photographs show that there is 
a corresponding reduction in the size of the leaf-trace. 
Such specimens seem to indicate clearly that the simpler type of stele 
characteristic of normal young stages in the ontogeny of Helminthostachys 
is to be associated with small size and less efficient nutrition. The same 
juvenile structure can be resumed when from any cause an adult rhizome 
becomes again feeble and more slender. 
4. On the Interpretation of the Construction of the Rhizome 
and Stele in Helminthostachys. 
In the preceding parts of this paper a number of facts have been 
described which amplify our knowledge of the anatomy of Helminthostachys . 
In the description of the facts theoretical interpretations have been touched 
upon as lightly as possible. Some general considerations may fitly be 
placed here, and are necessary in order to properly discuss Professor 
Campbell’s views on this plant. 
If the descriptions of the adult rhizome, the branches, and the young 
plants are compared, an essential similarity in construction will be found to 
underlie the differences presented by rhizomes of various sizes. As regards 
general morphology the rhizome is throughout dorsiventral, the ventral 
region bearing roots but no leaves, while the dorso-lateral leaves alternate, as 
shown by their leaf-traces, to either side of the middle line. In relation to 
each leaf is its vestigial axillary bud, which may be more or less displaced 
in front of the leaf-trace—in adult rhizomes usually by the whole length of 
the leaf-gap. There is thus a general indication of a segmental repe¬ 
tition of the parts of the shoot which will need to be considered further 
below. 
The essential agreement in stelar construction between the juvenile and 
adult rhizomes must first be made clear. If the series through the adult 
rhizome (Text-fig. 2) be considered, it will be evident that while the large 
pith is continuous from node to node it is unequally encroached upon by 
xylem at different levels. This especially concerns the inner xylem. The 
inner xylem, on the one hand, diminishes in amount (and often disappears), 
