THE MORPHOLOGY OF THE STELE OF PLATYZOMA MICROPHYLLUM, R. BR. 573 
clothing the leaf-trace-xylem on its outer surface had become thinner, no diminution 
of phloem took place at the points where the leaf-trace-xylem had freed itself. In 
point of fact, no sooner had an edge of the leaf-trace-xylem become free than 
phloem began to appear in the gap which separated it from the stelar'-xylem, and 
as the gap widened a sheet of phloem appeared in the parenchymatous mass beneath 
the leaf-trace-xylem. This sheet of phloem was an inward continuation of the 
stelar-phloem beneath the departing leaf-trace-xylem. It was destined to meet a 
similar phloem-sheet projecting through the gap which separated the leaf-trace- 
xylem from the stelar-xylem at the other edge, and when these phloem-sheets had 
met and fused, a continuous sheet of phloem was spread once more over this 
portion of the stelar-xylem. Meanwhile the local depletion of the outer xylem 
had been corrected, and the “external pit” had been obliterated. 
While these structural changes were proceeding, the leaf-trace-xylem and its 
accompanying crescent of phloem had continued their outward course, and the leaf- 
trace-phloem had become free from the stelar-phloem. The pericycle and outer 
endodermis had been moved outwards to accommodate the xylem and phloem of 
the leaf-trace, and when the limit of this accommodation was reached, the leaf- 
trace possessed a crescent of xylem with phloem on its convex surface and around 
its margins. 
When the gap in the peripheral cylinder of stelar-xylem had been repaired, and 
phloem again covered the xylem, a new endodermal formation appeared on both sides 
of the departing leaf-trace. Endodermal cells spread obliquely inwards from two 
points upon the arched outer endodermis, and having spread inwards, they united 
to establish a continuous endodermal wall which completely excluded the leaf-trace 
from the stele. No sooner had this endodermal formation been completed, than the 
outward arched portion of the outer endodermis which had accompanied the other 
components of the leaf-trace on their outward course became free as a crescentic 
band following the general outline of the trace. As a consequence of these modifica- 
tions the endodermis of the free leaf-trace was at this stage incomplete, being 
maintained upon the outer side of the trace, but absent from the inner side. This 
condition was not long maintained. An inner band of endodermal cells soon appeared 
completing the leaf-trace-endodermis upon its inner side. It was then evident that 
in the process of leaf -trace-formation and -departure, the inner endodermis was in 
no way involved ; and further, there existed no point where the stele was not entirely 
enclosed by an outer endodermis. Not only has it been demonstrated that in this 
plant — so far as the materials examined are concerned — there existed no ground- 
tissue-connection between the cortex and pith, but also that no connection existed 
between the cortex and the pericycle at the point of final liberation of the leaf -trace 
into the cortex, or at any other point. The possibility of such a connection had, 
in fact, been removed by the formation of the fused endodermal sheets as 
described above. 
