THE MORPHOLOGY OF THE STELE OF PLATYZOMA MICROPHYLLUM, R. BR. 583 
materially alters or helps to solve the problem of the origin of the pith and the 
nature of the stele of Platyzoma. On the other hand, the small specimen referred 
to above revealed some interesting features. These will now be described in 
advancing order as they presented themselves in the series of sections into which 
the stem was cut from its incomplete base to the apex. The series of illustrations 
of this plant given in the accompanying plates have been prepared by camera-lucida 
drawings, and are made to a uniform magnification. 
At the broken base of the stem the stelar structure was as in fig. 1. The 
outer endodermis (O.E.) was continuous, and root- and leaf-traces were being 
liberated (R.T. and L.T.). There was a narrow band of phloem (Ph.) around the 
bulky xylem. The latter was divisible into a narrow peripheral zone of small 
elements, and a mass of inner parenchymatous xylem much more bulky towards 
a t> c 
Text-fig. 1 . — Diagrams of the structure of the stele of Platyzoma at successive points in a 
bifurcating stem, as seen in transverse sections. Both outer and inner endodermis are 
represented by black lines ; phloem is hatched and xylem is solid black. Pericycle, 
inner parenchyma, and pith are white. ( x 12.) 
the lower than the upper side of the stele. The xylem enclosed a mass of parenchyma, 
the central part of which was surrounded by a small continuous endodermis (I.E.). 
This condition was followed by that shown in fig. 2. The bulky xylem was main- 
tained, and apparently isolated tracheides were found in the mass of parenchyma 
which it surrounded. The inner endodermis had closed down to form a narrow 
tube enclosing only a few rows of parenchymatous cells. A little in advance of the 
point where this latter condition was seen the stelar structure was as in fig. 3. 
The inner endodermis had been reduced to a vanishing-point, so that it appeared 
in section as a small group of endodermal cells enclosing no parenchyma (I.E.). 
In the immediately succeeding sections the stele appeared as in fig. 4. The inner 
endodermis had ceased to exist at this point, and a stelar structure in no way 
distinguishable from that of a medullated protostele had been established. This 
condition was followed almost immediately by that shown in fig. 5. The pith 
was no longer bulky, and a stelar structure not far removed from an almost solid 
protostele was seen. As the series was followed forward, the condition illustrated 
in fig. 6 was reached ; an irregular but continuous medulla had been created by a 
