718 
DR JOHN M‘LEAN THOMPSON ON NEW STELAR FACTS, 
(iii) No marked increase has occurred in diameter of the xylem-cylinder or stelar 
area during the transition from solid protostely to the medullated state. 
Thus the progression to the well-marked parenchymatous pith is accom- 
panied by reduction in transverse area of wood. The increase of stelar 
parenchyma is in this instance greater than that of conductive tracheides, 
the gain to the former constituting a loss to the latter. The inter- 
dependence of medullation and xylem-increase, and the intrastelar origin of 
pith in Schizsea malaccana, are thus indicated. 
The progression from the juvenile to the adult stele has not been traced, but 
the latter has been examined by Russow (.51), Prantl (50), Tansley and 
Chick (58). 
They have recorded a stelar structure similar to that shown in fig. 6, and were 
united in considering the intraxylic parenchyma “ an intrastelar pith.” The differ- 
entiation of the vascular system from the growing apex of the stem has been studied 
(58). The recorded facts are in harmony with the intrastelar theory for the pith, 
and in no way support the cortical hypothesis. Within the pith Tansley and Chick 
have found in plants with large steles, strands of tracheides the arrangement of which 
is “ quite capricious.” Thus the pith with internal tracheides described for the 
sporeling has been shown to recur in the adult. 
To other features which have been observed in adult stems of this species, 
and particularly the presence of endodermal pockets decurrent from the axils of leaf- 
traces through xylic gaps into the pith, further reference will be made., For the 
moment it may suffice to note that, though the ontogenetic development of these 
pockets has not been observed, they are absent from the medullated sporeling. It 
may then be held that in the ontogeny of Schizsea malaccana stelar pocketing is 
antedated by medullation. 
Schizsea dichotoma. 
A number of incomplete adult stems of this species have been examined.* In 
general they revealed a stelar structure similar to that already described by Boodle 
(3), (5). Throughout the greater length of stem examined the bulky sclerotic pith 
has a selvage of thin-walled parenchyma. For the most part the xylem-cylinder is 
solenoxylic, locally it is dictyoxylic, and xylic gaps independent of leaf-traces occur. 
In text-fig. 1 the general distribution of stelar tissues is shown in longitudinal section 
with leaf- and root-traces reduced to one plane. Endodermis is indicated by the line 
(En.), thin-walled-parenchyma is white, phloem cross-hatched, xylem solid black, and 
sclerenchyma dotted. Leaf-traces are lettered in ascending order (a, b, c, etc.), and 
levels specially mentioned are numbered. At I there is a xylic gap with shallow 
endodermal pocket, but no leaf-trace. In the axils of leaf-traces a, b, e, f, and g are 
* These have been kindly provided by Professor Margaret Benson, D.Sc., and Rev. W. W. Watts, F.L.S. 
