6 
Lang.—Studies in the Morphology and 
of the rhizome is less complete, the pith of the root appears continuous with 
that of the rhizome (cf. PL II, Photo 25). This occasional parenchymatous 
continuity between the pith of the rhizome and root is obviously of 
no significance as regards the nature or origin of the pith of the root. 
It is of some interest to find that an internal endodermis may be 
developed in the basal region of a root, delimiting its pith. Such an endo- 
dermal layer may be more or less complete. Its position in a well-marked 
case is shown in Text-fig. i, B. As in the case of the rhizome, the internal 
endodermis of the root may abut directly on the tracheides. There is 
clearly no reason to look on the internal endodermis of the root as anything 
but a new development, and its occurrence thus bears on the significance to 
be attached to the internal endodermis present in the rhizome. 
Origin and structure of the leaf-trace. It has been pointed out 
above that the dorsal side of the stele is of special interest, since the leaf- 
traces depart from it, and also because of the vascular disturbance in 
relation to the vestigial buds (cf. Text-fig. 1, B). As is well known, the 
departing trace leaves a long narrow leaf-gap in the medullated stele. 
This gap closes before the next leaf-trace separates, so that the gaps do not 
usually overlap, and their mutual relation is similar to what is found in 
many dorsiventral solenostelic Ferns. The vestigial bud discovered by 
Gwynne-Vaughan is situated just in front of the closed leaf-gap to which it 
belongs, and the vascular disturbance in relation to the bud is found just as 
the gap closes. The vascular disturbance thus lies alongside the separating 
trace for the next leaf (Text-fig. 1, B). A series of sections through the 
region of separation of one leaf-trace will thus show the closure of the 
preceding leaf-gap on the other side of the median line, and the vascular 
relations of the vestigial bud. Such a series from a large rhizome is repre¬ 
sented in Text-fig. 2 ; it shows to the left the earlier stages in the separation 
of a leaf-trace, and on the right the closure of the preceding leaf-gap, the 
development of the bulge of xylem in relation to the vestigial bud, and the 
return to the normal thickness of the vascular tube in front of this. Leaving 
the consideration of the vestigial bud to the next section, the origin, 
separation, and further history of the leaf-trace in this specimen may now 
be considered. 
This rhizome had a complete internal endodermis, and the inner meta- 
xylem was well developed. The first indication of the position and extent 
of the leaf-trace was afforded by the disappearance of the endodermal 
characters from the cells internal to the nascent trace. The xylem tube 
in the region of the trace also appeared thinner, owing to a less development 
of centripetal xylem. This is the condition reached at the level of the 
section in Text-fig. 2, A; the adjoining leaf-gap has begun to close, while 
the position of the nascent leaf-trace had been recognizable some distance 
behind the level of this section. The series of figures in Text-fig. 2 shows 
