720 
DR JOHN M'LEAN THOMPSON ON NEW STELAR FACTS, 
This is the closed base of the endodermal pocket decurrent from the axil of 
leaf-trace h, while the base of the trace itself is indicated. , by the protruding 
arc of xylem and phloem (Y). Fig. 9 represents a transverse section of the 
stele at a slightly higher level (III). Here the endodermal pocket is tubular, and 
contains thin-walled parenchyma like that of the inner cortex. The stelar core 
is no longer purely sclerotic, but comprises thin-walled cells (Z), among which 
endodermal cells occur (En.). These are the basal cells of the endodermal spindle. 
In fig. 10 the stelar structure at level IV is shown. The mouth of the pocket 
has been reached, but the leaf-trace is not yet free from the stele. An increased 
proportion of the intraxylic tissue is thin-walled parenchyma, here continuous 
from the stelar core to the pericycle through the xylic gap (G-). At this level 
the isolated endodermal spindle is a wide tube (En.) containing thin-walled cells 
like those around it. At V the leaf-trace has been freed from the stele, and the 
endodermal spindle in the pith has reached a vanishing point (En., fig. ll). Within 
the central parenchyma is a group of tracheides (T). The 'succeeding sections show 
no trace of the inner endodermis, but the inner tracheides are increased in 
number (T, fig. 12). 
Reduction of the xylem spindle marks the succeeding sections. Its vanishing 
point is reached in fig. 13 (T), and the pith is once more mainly sclerotic. 
All the structural facts accord with the view that the intrastelar changes in 
balance and distribution of wood, thin-walled parenchyma, sclerenchyma, and 
endodermis, thus traced from point to point, have been accomplished in the ontogeny 
by change of procambial destination as the growing point advanced, and that the 
tissues involved are of purely intrastelar nature. 
Isolated endodermal spindles within the pith have also been recorded, by 
Boodle (5), who, for lack of a ready explanation of their function as independent 
structures, suggested that they may be relics of foliar pockets, which, having figured 
in the ancestry, have lost their mouths during descent, and thus are no longer 
linked to the outer endodermis at stelar gaps. Tansley and Chick (58) have 
recorded not only deep foliar pockets but also an endodermal spindle within the 
stele of Schizasa malaccana. The latter structure is decurrent from the axil of a 
leaf- trace, but, though devoid of an opening into the cortex, is linked to the outer 
endodermis through the xylic gap by a chain of endodermal cells. It is undoubtedly 
a potential pocket, but its actual state and origin may be variously interpreted. 
It may indicate a phyletic degeneration of foliar pockets, or may merely illustrate 
how procambial destination determines mature structure. On the latter view an 
endodermal spindle initiated within the stele may in one instance be linked to the 
outer endodermis at a xylic gap, thus contributing to one unbroken endodermis ; in 
another such an endodermal union may be partial or absent. The central position 
of the endodermal spindle referred to in the adult stele of Schizsea dichotoma and its 
independence of adjacent leaf- traces give point to the latter suggestion. It is indeed 
