932 Lee. — Notes on the Anatomy and Morphology of 
of material available it has been impossible to ascertain whether the latici- 
ferous elements are vessels or cells ; from their appearance in section near 
the apex of the stem they appear to be the former. Some of the large 
parenchymatous cells of the pith contain much starch in the form of grains 
split in the centre (Fig. 3). These are aggregated in very large numbers in 
the cells around the medullary bundles and laticiferous elements, being 
comparatively scarce in the other cells of the pith. Sclerosis and the forma- 
tion of islands of soft bast, both of which are characteristic of Apocynaceae, 1 
are absent from the pith in Pachypodium. The medullary bundles (Fig. 2) 
are composed of scalariform xylem elements and phloem, with a little 
parenchyma lying between the two. They are always accompanied by 
laticiferous elements (d, Fig. 2), which usually lie next to the xylem. 
Unlike those of some Apocynaceous plants, they have no definite orienta- 
tion. They are given off by the vascular ring into the pith ; owing to the 
lack of young material it has 
been impossible to ascertain 
whether they owe their origin 
entirely to the ring bundles or 
not. They pursue a most irre- 
gular course in the pith, both 
branching and anastomosing so 
as to penetrate every part of 
it. When a portion of the pith 
is macerated the medullary 
bundles alone are left, forming 
a complex network. The lati- 
ciferous cells branch and run in 
all directions through the pith, 
In a transverse section of the 
stem they are seen to enter the pith from the cortex through the medullary 
rays (Fig. 4), as in many other members of the order. 2 
The vascular bundles of the ring are collateral ; very little wood is 
present, and the medullary rays are broad (Fig. 4). The xylem is com- 
posed of scalariform elements and parenchyma; cambium is present (c, 
Fig. 4), but the small amount of secondary tissue formed by it remains 
parenchymatous. The phloem (b, Fig. 4) consists of narrow sieve-tubes 
with sieve-plates on their terminal walls. The apparent absence of intra- 
xylary phloem is very striking, for in all other investigated genera of 
Apocynaceae it has been found. 3 Mr. Worsdell suggests that the intra- 
xylary phloem bundles are present, but that they possess xylem, hence 
the medullary bundles. Evidence in support of this view will be given in 
the description of the structure of the protuberance and the petiole. No 
1 Solereder ( 5 ), p. 531. 2 1 . c., p. 530. 3 1 . c., p. 531. 
Text-fig. 3. Diagrammatic transverse section of 
petiole, showing the arrangement of vascular tissue. 
a. xylem ; b. phloem ; S. starch sheath. 
either with or separate from the bundles. 
