in the 'Seedlings' of Certain Leptosporangiate Ferns . 367 
phloem, so that at this level we have a relatively broad band of xylem 
surrounded externally by phloem, and containing at its centre a core of 
phloem in which the sieve-tubes appear as a central strand surrounded by 
two or three layers of phloem parenchyma. The pericycle consists of 
a single layer of cells whose radial walls are not in regular seriation with 
those of the somewhat poorly differentiated endodermis. The fundamental 
tissue is composed of parenchyma containing a considerable amount of 
starch, and, in young plants at any rate, is characterized by a complete 
absence of the sclerenchyma which is so striking a feature in the seedlings 
of some other ferns. 
The first leaf-gap is formed in a very simple manner, a sector of the 
vascular strand becoming detached and passing outwards as the leaf-trace. 
On the completion of the trace, the external and internal phloem become 
continuous round the horns of the xylem arc, by the differentiation of 
sieve-tubes at these regions. The endodermis merely bridges the leaf-gap, 
there being no indication of any ‘dipping in’ of this layer (Fig. 200). It 
is somewhat difficult to decide whether the internal phloem ‘ takes any part 
in ’ the formation of the leaf-trace, but the evidence points to such being 7 
the case ; expressed more correctly, the leaf-strand is concentric even at 
its junction with the cauline system, the adaxial moiety of its phloem being 
continuous with the internal phloem strand, and the abaxial portion with 
the external phloem sheath of the vascular arc. During the separation of 
the leaf-trace, a root-strand joins the cauline system at a point almost 
exactly opposite the leaf, its junction taking place in a perfectly simple 
way. Very soon after the completion of the leaf-trace, the gap is closed 
in the well-known manner by the gradual extension of the horns of the 
gap towards one another, the result being the appearance of a ring of 
xylem surrounded by phloem, and enclosing a central strand of sieve-tubes 
and parenchyma (Fig. 201). It should be noticed that there is no internal 
endodermis or phloeoterma. The sieve-tubes still form a solid core in the 
internal phloem, but this condition of things is not long maintained, for 
very soon preparations are made for the exit of the second leaf-trace, and 
at this point a few parenchyma cells appear in the core of sieve-tubes. 
It is still noticeable, however, that the latter are by far the most numerous 
and conspicuous elements of the intraxylary tissue. 
In the majority of cases, the second leaf-trace is formed in exactly the 
same way as the first, although individual variations are frequent. The 
corresponding root-strand then joins the vascular system. The third and 
fourth leaf- and root-traces are formed in a perfectly normal manner, but 
in connexion with the fourth leaf-gap we have, for the first time, a differ- 
entiation of a blunt projection of ground-tissue between the edges of the 
gap, the ground-parenchyma being separated from the vascular tissue by 
a continuation of the normal endodermis. In other words, the endodermis 
