Affinities of Helmintkostachys zeylanica . 441 
xylem-parenchyma, which is dilated somewhat in this region, 
serving as the link between them. 
In transverse section the roots are seen to be most com- 
monly hexarch, though different roots vary in this respect 
from tetrarch (rare) to heptarch. In respect of the number 
of its xylem- and phloem-groups in the root, Helminthostachys 
stands somewhat isolated from the rest of the Ophioglosseae, 
in which the number is much smaller ; whilst on the other 
hand it approximates more to the Lycopodiaceous type, 
many of the plants in this group possessing complex root- 
strands. The Marattiaceae, which are likewise noted for the 
numerous bundles in their roots, may also be kept in mind, 
although, as will have already been rendered evident, in nearly 
all essential features there exists no real similarity between 
them and Helminthostachys . There is a very well-developed 
central pith, and the sieve-tubes in the phloem are easily 
recognized. Outside the vascular elements there is a sudden 
transition to a layer of large-celled pericycle, which in its turn 
is enclosed in a tolerably distinct endodermis. 
The bulky cortex consists of rounded parenchymatous cells 
with prominent intercellular spaces between them. The 
cells of the outer cortex are more closely united, and in 
passing to the peripheral layers the intercellular spaces 
altogether disappear. The outer wall of the peripheral band 
of the cortex is thickened .and of a brown colour, and is 
distinctly suberised. 
In longitudinal section the apex of the root beneath the 
root-cap is found to be occupied by a single apical cell of 
triangular form, from which segments are cut off parallel to 
the four sides in the ordinary way. The segments however 
cannot be recognized individually save when very young. 
In this respect, as in so many others, the behaviour of the 
other Ophioglosseae is once more recalled. 
It very often happens that the apical cell is destroyed, 
either owing to the attack of some organism, or to a de- 
generation which owes its existence to causes inherent in the 
root itself. A very complex arrangement then frequently 
