84 Gwynne- Vaughan. — Observations on the 
sclerotic fibres are found in greatest quantity at the inner 
side of the phloem along the flanks of the horseshoe, and 
especially in the bays formed by the hooked ends of the 
xylem. One or two layers of the same accompany the concave 
internal surface of the xylem-strand, entirely replacing the 
phloem in the median region, and a few also occur on 
the external convex surface, forming an interrupted layer 
between the xylem and the phloem (Figs. 5 and 6, sc. t.). 
Fibrous elements, almost identical in position and appearance 
with those of Loxsoma , have been carefully described in the 
petiole of Aneimia Phyllitidis by Prantl 1 , who regards them 
as belonging to the phloem. Poirault 2 goes further; for he 
considers some very similar elements he observed in the 
petioles of certain Gleichenias actually to represent sieve- 
tubes which have undergone sclerosis. Evidence is not wanting 
which would lead to a similar conclusion with respect to the 
fibrous elements in Loxsoma. In the first place, the position 
that they occupy in the meristele relative to the other tissues 
is precisely that of sieve-tubes, and, wherever they occur in 
mass, thin-walled parenchyma-cells are scattered amongst 
them, which may be regarded as representing the phloem- 
parenchyma (Fig. 6 , pa). Again, towards the base of the 
petiole they gradually decrease in number (those in the bays 
of the hooks persisting longest), until at the point where 
the leaf-trace enters the tissue of the stem they disappear 
altogether, their place being progressively taken up by 
undoubted sieve-tubes. They are usually separated from the 
xylem by a layer of thin-walled parenchyma, but occasionally 
are found in direct contact with a tracheide (Fig. 6 , at +). 
This, however, does not affect our comparing them with 
sieve-tubes, because the latter are also sometimes found in 
the same position, both in Loxsoma and in other Ferns. 
Moreover, as seen in Loxsoma , these fibrous elements closely 
1 Untersuch. z. Morph, d. Gefasskrypt., Heft ii, Schizaeaceen, p. 28 (Leipzig, 
1881). 
2 Recherches Anat. stir les Crypt. Vase., Ann. Sc. Nat., ser. vii, tome xviii, 
p. 190, and Fig. 18, 1893. 
