THE MORPHOLOGY OF THE STELE OF PLATYZOMA M1CROPHYLLUM, R. BR. 585 
pith thus formed expanded rapidly as the advancing series was followed, and within 
it a new endodermal formation arose (I.E., fig. 17). It passed quickly from this 
irregular and ill-defined condition to that seen in fig. 18. At all points the inner 
endodermal cylinder had become complete and fully differentiated. It embraced 
a large body of the medulla, part of which had become sclerotic. Further forward 
the stele as a whole underwent diminution (fig. 19), but later it expanded to the 
condition shown in fig. 20, having a wide and complete inner endodermal tube 
enclosing a somewhat sclerotic portion of the pith. At this point the stele showed 
the general structure which has hitherto been known for Platyzoma. 
It will be seen that so far as the description of this stem has gone, the inner 
endodermis has twice been narrowed down to a vanishing point, so that a stelar 
structure not distinguishable from a medullated protostele has been established 
locally. In the second place, it will be clear that with the increase in the medullation 
of the two protostelic zones thus formed an inner endodermis has arisen de novo within 
the pith itself. In both instances the diminishing endodermal tube has retained 
an unbroken identity to the end, but in the process of endodermal-re-creation there 
has been at first a marked indefiniteness. The new endodermis has not appeared 
within the growing pith as its predecessor vanished from the diminishing pith, for 
there is no single point of endodermal-re-creation from which an immediately tubular 
endodermis has expanded, whereas there was in both instances a single point to 
which the decreasing tubular endodermis was narrowed. It will be further noted 
that, in the first instance of re-establishment of the inner endodermis, the fluctuations 
preceding the establishment of a clearly tubular endodermis were prolonged and 
varied, but in the second instance they were few and comparatively simple. The 
two zones in which the protostelic state existed, and that portion of the stele where 
considerable constriction occurred (fig. 19), were the main points of origin of the 
small leaf-traces, while those zones which possessed a large pith gave rise to the 
majority of the large leaf- traces. It was difficult to determine the destination of 
each leaf-trace even in a careful reconstruction of the stem, but the opinion was 
formed that the protostelic zones coincided roughly with two of the groups of 
small leaves. 
The general construction of the most interesting portion of the stele of this plant 
is illustrated in text-fig. 2. It purports to represent in slightly simplified form the 
general proportions and relationships of the component tissues as seen in median 
section. The outer and inner endodermal layers are indicated by black lines, both 
pericycle and pith are white, phloem is hatched, and xylem is solid black. It will 
be seen that throughout the greater part of the stele thus represented, the protostelic 
zones show conspicuous increase of the xylem towards the lower surface of the stele. 
An examination of the figures given in the plates of this paper will show that this 
increase is due to marked local increase of the parenchymatous inner xylem. 
Throughout the entire length of stem so far described neither foliar gaps nor 
