32 Lang .— Studies hi the Morphology and 
all that need be done is to refer to the progress in size and in stelar 
complexity. 
This piece of rhizome measured about an inch and a half in length, and 
rapidly increased in diameter from the narrow basal end till its full diameter 
was attained and then maintained. Its diameter at the base was slightly 
over 2 mm. and the diameter of the adult region was about 7 mm. A 
transverse section at the base (Text-fig. 8, a) showed the xylem of the first 
leaf-trace already separate from the stelar xylem, but within the common 
endodermis. The xylem of the stem stele was complete, showing no 
indication of a gap, and at this level was practically solid, only a few 
parenchyma cells being scattered among the more central tracheides. There 
were indications of a distinction between somewhat smaller tracheides of 
the inner xylem and the zone of outer xylem, though the limit was not easy 
to decide definitely from transverse sections. Where the sections were 
slightly oblique, it could be seen that the inner tracheides were spirally 
thickened and those of the outer xylem pitted. The stele at this level, 
though larger than the other examples described, was thus of the juvenile 
type. The xylem of the departing first leaf-trace was clearly endarch. It 
did not show adaxial completion, and indeed as it became further removed 
from the stele ceased to be lignified; it was evidently related to an 
arrested leaf. 
Meanwhile, parenchyma had become more definitely present in the 
central region of the stele, replacing some of the inner xylem and forming 
a small pith, around which a broken ring of elements of the inner xylem 
remained. The distinction between the outer and inner xylem was evident 
on the appearance of the protoxylem of the second leaf-trace, which had 
elements of inner xylem internal to it. Then the inner xylem disappeared 
opposite to the nascent endarch trace, the pith being continuous into the 
concavity of the latter. The xylem of the trace, derived from the outer 
xylem only, almost closes round as it separates from the xylem of the stele 
(Text-fig. 8 , C). The adaxial closure becomes complete later, and this trace 
passed through the usual clepsydroid stage and divided just before it 
departed from the cortex. While the separation of the second trace has 
been proceeding, the stele has enlarged and is provided with a greater 
definite pith. The inner xylem is especially well represented as the 
gap closes. 
It is unnecessary to follow the elaboration of the stelar structure 
further in this rhizome, but this portion is of interest in showing how, 
between the departure of the first and second leaf-traces, the xylem passed 
from the solid condition with inner and outer xylem to the definitely 
medullated condition found in small rhizomes of the adult type of structure. 
It is impossible to state at what level the inner xylem was composed of 
pitted tracheides, but it was evidently by now or not much further on. The 
