D at hie. — Anatomy of Gnetum africanum. 595 
were also noticed (PI. LVIII, Fig. 8, a-d). The later formed vessels 
usually have inclined end walls with a single oval or circular perforation 
(Fig. 8, e-f ). In one case two large circular openings were observed. 
In transverse sections the remains of the oblique septa of the vessels with 
their perforated bordered pits are often seen (PI. LVII,Fig. 1). Associated 
with the true vessels of the secondary xylem are numerous gymnospermous 
tracheides. The thickness of the walls and the size and shape of the 
bordered pits in both vessels and tracheides vary considerably. In addition 
to the tracheal elements large numbers of elongated cells with protoplasmic 
contents and simple pits occur in the secondary xylem. They do not contain 
starch, but occasionally numerous minute crystals of calcium oxalate are found 
in them. Near the cambium these parenchymatous cells are usually seen to 
be arranged in regular rows continuous with the albuminous cells in the 
phloem (PL LVIII, Figs. 9, 12 ) ; in the older wood they are scattered, 
apparently owing to the enlargement of the vessels. Occasionally, the 
lumina of the vessels were found to be blocked with resinous substances. 
Phloem. The boundary between the xylem and phloem masses of the 
vascular bundles, as seen in transverse section of the younger internodes, has 
the shape of an arc whose concave side is directed outwards. In older 
internodes this appearance is generally lost. The phloem elements are 
extremely regular ; 1 but when sections are placed in water, considerable 
swelling and distortion occurs. No hard bast elements are present. The 
large sieve tubes are arranged in radial rows (Figs. 9, 10, 12). Compound 
sieve plates occur in large numbers on the very oblique end walls, but 
are less numerous on the vertical walls (Figs. 13 and 14). On staining with 
iodine after heating in glycerine, minute starch grains may be seen in the 
albuminous contents of many of the sieve tubes. Considerable callus 
formation covers the older sieve plates (Figs. 15 , 17 , 18). These callus 
pads stained readily with water blue, Russow’s callus reagent, and corallin 
soda, but were unaffected even after prolonged staining with aqueous solu- 
tions of aniline blue and eosin. Particularly good results were obtained 
with water blue. 
The albuminous cells are also arranged radially, and, as was remarked 
above, they are generally continuous with the elongated parenchymatous 
cells of the xylem (Fig. 12). In longitudinal section they are seen to be long 
and narrow, with dense proteid contents and well-defined, often elongated, 
nuclei (Fig. 14). Their end walls are at first transverse, but later become 
oblique. Numerous minute crystals of calcium oxalate are often collected 
at one end of these cells, and small starch grains are occasionally present. 
A doubling of the radial rows of albuminous cells and sieve tubes 
often takes place. In the older phloem, owing to the displacement of the 
elements, the albuminous cells come to lie at the corners of the sieve tubes 
1 Boodle and Worsdell (1). 
