THE MORPHOLOGY OF THE STELE OF PLATYZOMA MICROPHYLLUM, R. BR. 591 
In leaf-trace-formation and -departure the inner endodermis was in no way involved, 
and no point existed where the stele was not entirely enclosed by an outer 
endodermis. 
The theoretical statements which have been made regarding this stelar structure 
are then considered. They have been advanced by Dr Poirault, Dr Jeffrey, Mr 
Boodle, and Mr Tansley. It is shown that in first suggesting that the pith of 
Platyzoma is the result of confluence and final isolation of a series of foliar sclerotic 
pockets, Dr Poirault imagined certain non-existing conditions as fulfilled in a 
Grleicheniaceous plant and merely contemplated through them a possible explanation 
for Platyzoma. He did not profess to support his interpretation by actual structural 
evidence from the plant itself. To Dr Poirault’s conception of the stelar structure 
support has been given by Dr Jeffrey and Mr Tansley. The former has affirmed 
that the pith of Platyzoma is in reality of extrastelar origin, or is at least most 
reasonably interpreted as such, though as a result of stelar reduction it no longer 
communicates with the peripheral cortex. Mr Tansley has held that there is reason 
for considering the stele of Platyzoma as reduced from an original solenostele by 
loss of internal phloem and leaf-gaps. Dr Jeffrey has further claimed to have 
observed nearly degenerate leaf-gaps in the stele. It is shown that in none of the 
materials so far examined is there structural evidence which can be reasonably 
advanced to support a belief in the present reduced state of the stele of Platyzoma 
or of its present or prior possession of foliar gaps. As an alternative interpretation 
of the stelar structure Mr Boodle has suggested that the medullated stele of 
Platyzoma may possibly have been derived from a protostelic origin by the direct 
formation of an independent intrastelar pith and inner endodermis. 
It is held by the present author that the evidence so far advanced is inadequate 
to allow of a confident opinion regarding the nature and origin of the medullated 
stele of Platyzoma. For while no evidence of the intrastelar origin of the pith 
and inner endodermis has emerged to support Mr Boodle’s suggestion, the reduction 
theory is not supported by the demonstration of cortical “ intrusion ” into the stele 
through stelar gaps, nor by the presence of stelar gaps and a solenostelic condition. 
The reduction hypothesis seems to stand upon the more comprehensive assumptions, 
but neither view can claim to be considered to indicate more than the undemon- 
strated possibilities. 
A description of the stelar structure of a number of recently acquired incomplete 
specimens of Platyzoma follows. It is shown that in the majority of these the 
stelar-structure was identical in plan with that already described. Neither a 
solenostelic condition nor evidence of degenerate stelar gaps or inner phloem was 
found. The investigation of these plants added nothing to our knowledge which 
materially alters or helps to solve the problem of the origin of the pith and the 
nature of the stele. But on the reduction hypothesis they might be considered 
evidence of the firm establishment of the reduced condition, while on the theory of 
