Affinities of Helmint ho s tacky s zeylanica. 431 
as depressions in the swollen walls, and they are divided 
up into still smaller areas or pits, much as in the case of 
the pits in the cortical parenchyma alluded to above. Con- 
tinuity of the protoplasmic contents of two contiguous sieve- 
tubes can be fairly easily demonstrated, and it is then 
seen that the membranes of the individual pits (which 
collectively make up a plate) are pierced by very fine holes 
through which the protoplasmic strands pass across. When 
the sieve-tubes are isolated, by macerating the tissues, they 
are seen to possess a firm internal membrane which is con- 
tinuous with that forming the pits, and the swelling is proved 
to be due to a substance which dissolves away in the Schultze’s 
fluid employed to separate the cells. The pits then appear 
of course as protrusions of the cell-wall (see Fig. 20, PI. XXIII) 
since the intervening substance has been cleared away in 
solution. 
In many instances it seemed almost certain that there was 
a sieve-connexion, not only between the sieve-tubes them- 
selves, but also between the tubes and the parenchyma of 
the phloem. If our observations on this point are correct 
it would seem that the parenchyma in this Fern can function 
as companion-cells, as has been stated by some investigators 
for other Ferns. But there is no evidence here of the (possibly) 
functional companion-cells having been derived together with 
the sieve-tube, from a common mother-cell, and therefore 
the arrangement is one of physiological interest only. The 
sieve-tubes are differentiated and easily recognizable imme- 
diately behind the apical meristem ; they are separated by 
a rather broad band of parenchyma from the xylem of the 
stele. 
The wood of this stem presents several points of interest. 
In the first place the protoxylem-elements are not developed 
on the inner side of the ring, as in the other Ophioglosseae, 
nor at its outer side as in those Selaginellas 1 which, e.g. S. 
laevigata , var. Lyallii , bear some resemblance to Helmintho- 
s tacky s in respect of their steles. They are differentiated 
1 Harvey Gibson, loc. cit. 
