48 Lang.—Studies in the Morphology and 
plants by revealing additional and unsuspected resemblances in the morpho¬ 
logy and anatomy of the stem and leaf-trace. If our knowledge of the 
anatomy of Helminthostachys was based on the four pieces of rhizome illus¬ 
trated in Text-figs. 2, 3, Text-fig. 4, Text-figs. 5 and 6 , and Text-fig. 8, it 
may reasonably be stated that we should find our closest comparisons not 
among existing Ferns, but with the palaeozoic Zygopterideae and Cycado- 
filices. If these resemblances indicate the true affinities of the isolated 
group of the Ophioglossaceae, the latter present an interesting contrast, as 
regards the evidence, to the Osmundaceae, which there is also reason to 
trace back to the ancient Fern stock. In the case of the Osmundaceae 
we have fossil remains extending our knowledge of the group back to 
Permian times. In the Ophioglossaceae the conclusion that there is a true 
affinity with Zygopterideae seems, if anything, more inevitable in the light 
of the primary structure of the stele, the secondary thickening, the structure 
of the leaf-trace, and the nature of the branching. The evidence is here 
derived from comparative anatomy with a practical absence of any historical 
record between the early palaeozoic Ferns and the Ophioglossaceae of the 
present day. 
Summary. 
1. The rhizome of Helminthostachys exhibits a general segmental con¬ 
struction, and may be regarded as composed of three series of segments, 
one ventral and two dorso-lateral. The insertion of a leaf, with its stipular 
sheath and axillary bud, corresponds to each dorso-lateral segment, the 
leaves alternating right and left of the median line. The ventral segments 
do not bear leaves. This arrangement holds throughout the plant. 
The transition from a leaf into its region of the stem is a gradual one, 
and it is hardly possible to speak of definite internodes in the adult plant. 
In the slender shoots of young plants the leaf insertions are more separate 
and internodes may be distinguished, at least in the stelar anatomy. 
It is not stated that the segmental construction of the rhizome is 
related to the cell-segmentation at the apex, though it would be consistent 
with such an explanation. 
2. The stele of the adult rhizome has a large pith, and the tube of 
xylem around this is mesarch, i. e. consists of outer and inner xylem, the 
protoxylem elements being found between them. The inner xylem may 
be more or less extensively represented ; in smaller rhizomes there may 
only be scattered tracheides at the periphery of the pith, and sometimes the 
latter abuts directly on the protoxylem. 
3. The roots are endogenous, but only penetrate a comparatively thin 
zone of cortical tissue. The xylem of the root is continuous with the outer 
xylem of the stele of the rhizome, and when the inner xylem of the latter 
