in the ‘ Seedlings * of Certain Leptosporangiate Ferns . 395 
strands divides into two (Fig. 47) and the subsequent union at a higher 
level, indicated in Fig. 48, takes place. The fourth leaf-trace is double at 
its origin (Fig. 49), but before it enters the leaf-stalk the two strands have 
united. In Fig. 50 we have three cauline strands, and at higher levels in 
older plants several appear in a transverse section of the stem. The increase 
in number is, of course, due to the division of the vascular strands before 
the previous leaf-gap has been repaired, and the repetition of such a process 
results in the dictyostelic arrangement of the vascular system of adult plants 
being attained. 
The leaf-traces maintain their double character for successively longer 
periods, with the final result that the petioles of the later leaves possess two 
or more strands. 
Nephr odium hirtipes has previously been examined by Jeffrey, and 
referred to by that author in his Royal Society memoir h The details of 
the vascular development, however, were not described. 
Asplenium nidus, L. 
The vascular strand of the young primary root is extremely small, 
consisting of but a few sieve-tubes arranged on either side of a minute 
xylem plate. The first leaf-trace is given off quite early, before the xylem 
has lost its diarch character, and is quickly followed by a root-trace. The 
leaf-trace arises merely as a nipping off of one of the protoxylem groups, 
and is formed in a manner very similar to that obtaining in Polypodium 
aureum. As is so generally the case, the first few leaf-traces are of simple 
structure, consisting of two or three tracheides surrounded by a single layer 
of poorly differentiated sieve-tubes. The corresponding root-traces are much 
more definite, the well-marked endodermis being particularly conspicuous 
when the rootlets are viewed transversely. 
A certain amount of variation was met with in the early transitional 
region. In a few cases, the first two or three leaf- traces were formed before 
a central pith of phloem had appeared in the xylem strand (cf. Todea 
Fraseri 1 2 , Lygodium 3 , and Angiopteris 4 ), but, generally, parenchyma cells 
and extremely well-marked sieve-tubes were differentiated at the centre of 
the xylem immediately after the first leaf-trace. Higher up the stem the 
central phloem increases in* quantity, and after the second leaf-gap has 
closed in the usual manner, a transverse section of the stem presents the 
appearance found to be so common in the other plants investigated, viz., 
a ring of xylem surrounded by phloem, and enclosing a strand of phloem 
1 Jeffrey, Structure and development of the stem in the Pteridophyta and Gymnosperms. 
Phil. Trans., ser. B., cxcv, 1902, p. 131. 
2 q. v. 3 Boodle, Schizaeaceae. Annals of Botany, xv. 
4 Farmer and Hill, On the arrangement of the vascular strands in Angiopteris evecta. Annals 
of Botany, xvi. 
E e 2 
