in the ‘ Seedlings' of Certain Leptosporangiate Ferns . 397 
Aspidium falcatum, Sw. 
The young plants are characterized by the total absence of scleren- 
chymatous ground-tissue, even in the rootlets. The transition from the 
diarch root to the protostele extends over a considerable distance, and, as 
in Nephrodium setigerum , the completion of the phloem sheath is delayed 
for some time. The xylem of the protostele forms a very small rod of 
tissue, at the centre of which parenchyma cells are differentiated, quickly 
succeeded by very obvious sieve-tubes. 
The first lateral rootlet generally effects its junction with the stem just 
before the exit of the first leaf-trace, which is formed in a perfectly normal 
manner, leaving a small gap bridged by the endodermis. In examining 
a large number of seedlings, some little variation was observed in connexion 
with the formation of this leaf-trace, a variation occurring more than once 
being represented in Figs. 1 29-1 32. It will be seen that the xylem ring has 
opened, and that from one horn a concentric strand of vascular tissue is 
nipped off which passes outwards as the leaf-trace. In the majority of 
cases, however, the trace was perfectly normal, and on repair of the gap 
a ring of xylem enclosing and enclosed by phloem constituted the cauline 
strand. 
The second and third leaf-traces are formed in rapid succession nearly 
opposite one another, the gaps closing almost immediately. Their exit 
is followed by a long internode, and then another pair of leaf-strands is 
differentiated. This regular alternation of long and short internodes held 
true for all the comparatively young plants examined. 
In connexion with the fifth trace we have the appearance of a ground- 
tissue pocket. The internal sieve-tubes arrange themselves towards the 
periphery of the internal phloem and therefore lining the xylem, and in 
the central parenchyma a poorly differentiated patch of endodermal cells 
appears, which, a little distance above, surrounds a strand of ground-tissue, 
the latter becoming continuous at the leaf-gap with the main mass of funda- 
mental parenchyma. After the completion of the trace, another leaf-strand 
is formed exactly opposite the last, and the cauline system then consists of 
two strands which finally fuse. 
Unfortunately, older plants were not available, but the above phenomena 
are so similar to those described for other types that there can be little 
doubt that the subsequent fractionation of the vascular tissue takes place 
in a manner similar to that already described. 
Pteris PALMATA, Willd. 
The transitional changes are of the usual type. The root is diarch, 
the xylem plate rapidly becoming circular in section and surrounded 
by the phloem. The appearance of phloem in the protostele takes place 
