Anatomy of Solenostelic Ferns : I. Loxsoma. 89 
adaxial surface of the meristele, until it comes to occupy 
the bottom of a deep bay between the arms of the xylem, 
which for some time have been gradually approaching each 
other until they are now almost in contact. At length, 
therefore, owing to its diminished size, and to the flattening- 
out of its formerly concave side, the form of the meristele 
has changed by degrees from that of a horseshoe to that 
of an equilateral triangle with rounded angles and convex 
sides, the adaxial side being slightly indented at the centre 
(Fig. 7, d , and Fig. 8). Nevertheless, an indication of the 
form it originally possessed is still to be perceived in the 
curve that is retained by the xylem-strand, even when 
the outline of the meristele itself has become elliptic. While 
these changes are progressing the cavity-parenchyma be- 
comes less and less distinct, disappearing altogether before 
the meristele becomes elliptic. The sclerosed sieve-tubes, 
on the other hand, are still to be observed in considerable 
quantity (Fig. 8), and continue to persist even in the small 
veins of the lamina itself. The vascular strands of the lateral 
branches of the leaf pass through exactly the same changes 
until the ultimate ramifications of the veins in the foliar 
segments are reached : there they exhibit a perfectly col- 
lateral structure, the phloem being confined to the abaxial 
side of the xylem, at the adaxial extremity of which is 
situated a single protoxylem-group (Fig. 7, e). Although 
the mesophyll of the lamina is of considerable thickness, no 
palisade arrangement of the cells is to be found in it. On 
the contrary, they are all arranged in a loose spongy manner 
with numerous intercellular spaces, which, however, are par- 
ticularly large towards the under surface of the leaf. The 
cell-walls limiting these intercellular spaces are closely beset 
with those intercellular rodlets already described in the stem. 
The veins in the lamina are connected to both the upper 
and the lower surfaces by stout strands of sclerenchyma after 
the manner of girders, even the epidermal cells overlying 
these veins are more or less thickened and elongated in the 
direction of their course. The cells of the general epidermis 
