in the ‘ Seedlings ' of Certain Leptosporangiate Ferns. 369 
NEPHRODIUM SPINULOSUM V. DILATATUM, Hk \ 
The series of changes occurring in the transitional region of this plant 
resemble those of Doodia aspera , and need be described in no great 
detail. 
The primary root is diarch, and somewhat quickly passes into the 
protostelic condition. A few parenchyma cells, followed later by one or 
two well-marked sieve- tubes, appear at the centre of the xylem strand, 
their appearance being succeeded by the differentiation of the first leaf- 
trace, which takes place in the simple manner described above for the 
previous fern. The gap remains open through a considerable distance, and 
only closes just before the exit of the second leaf-trace. The phloem is 
continuous round the edges of the gap, and, on the closing of the latter, the 
cauline system consists of an amphiphloic vascular rod. The pericycle 
consists of relatively large squarish cells ; it is somewhat variable in thick- 
ness, not only at any one particular level, but also at different parts of the 
plant, a double layer of cells often persisting through several consecutive 
sections. The endodermis is narrow, but very conspicuous. 
The first three or four leaf-traces are differentiated in the same simple 
manner, and involve the formation of no real leaf-gap, the break in the 
vascular system being merely bridged by the endodermis. After the exit 
of about the fourth leaf-trace, however, the gaps become more pronounced, 
and at the level of the sixth leaf the xylem has assumed the shape of 
a curved band, into the bay of which the endodermis ‘ dips ’ sharply. The 
phloem, especially that portion of it lining the concavity of the xylem, is 
particularly well differentiated. 
At a slightly higher level, the seventh leaf-trace leaves the cauline 
system as the central portion of the curved vascular band, with the result 
that, after the exit of the trace, the stem is supplied with two concentric 
vascular strands, each surrounded by a separate endodermis. 
The xylem of the last-mentioned leaf-trace has a distinctly bilobed 
character — an indication of the double or multiple nature of the later- 
formed traces. 
After the closing of the seventh leaf-gap, the vascular arc again breaks 
into two portions, and the next leaf-strand is double at its origin, though 
single before it enters the leaf-stalk. By the splitting of one of the vascular 
strands before the previous gap has been repaired, we have the appearance 
of three concentric strands in the cauline system at this particular level, and 
later elaborations of an exactly similar type quickly result in the adult 
dictyostelic structure being reached. 
Hooker, Species Filicum, iv, p. 127. 
