in the ‘ Seedlings ' of Certain Leptosporangiate Ferns. 389 
Nephrolepis cordifolia, Baker (N. tuberosa, Hk.). 
The upright, sometimes horizontal, rhizome of this fern gives rise to 
numerous thin runners or stolons, which bear at intervals scaly tuberous 
bodies, and many branching adventitious roots. The stolons themselves, 
especially when young, are often more or less tuberous, and vary in 
thickness in different parts of their length. 
The root exhibits the usual diarch structure, possessing a well-marked 
endodermis, and a pericycle of varying width. The cells of the cortex are 
not sclerosed to any remarkable extent. The early transition to a solid 
protostele takes place in the usual way, the stem bending somewhat 
sharply at this region ; this is by no means an uncommon occurrence, 
as pointed out elsewhere. A few parenchyma cells are differentiated 
in the centre of the protostele, and the first leaf-trace is then given off. 
The trace consists of but a few elements, being practically a continuation of 
one of the protoxylem groups of the cauline strand together with a little 
phloem. The leaf-gap is very small, and, in one or two plants examined, 
no gap at all was left by the first leaf-trace. The external phloem at this 
stage is poorly differentiated, the identification of the sieve-tubes being 
a matter of considerable difficulty. This fact probably explains the 
apparent absence of sieve-tubes in the central pith until after the third leaf- 
trace, a state of affairs somewhat at variance with that found in the majority 
of other ferns examined. It frequently happens, however, that the pith 
is continuous with the external phloem by means of parenchymatous 
strands extending through the xylem, and in all probability the pith 
is really to be regarded as phloem in which the sieve-tubes are by no 
means well differentiated. 
The first three leaf-traces are formed in the simple manner indicated 
above, and the accompanying root-traces join the cauline strand in the 
usual way. Soon, however, the latter begins to increase in size, though it 
is still quite small and presents two protoxylem groups which are in much 
the same position as the protoxylem groups of the root. The pericycle 
now becomes more definite, and is usually two rows deep, its outer cells 
fitting exactly upon those of the endodermis. At this level, the vascular 
tissue supplying the first stolon is differentiated, and joins the cauline 
system in a way very similar to that of a root ; in fact, in a cursory 
examination, it is merely its size which distinguishes the stolon-strand from 
a root-trace. Its structure, however, is very similar to that of the stem at 
this level, except that a definite central pith is not present, parenchyma 
cells occurring scattered throughout the xylem. The stolon itself may be 
regarded as the result of an abrupt branching of the stem. 
After the junction of the stolon with the stem, the cells of the pith 
(which up to this level have frequently had a somewhat scattered arrange- 
