SECRETORY CANALS OF RHUS DIVERSILOBA 
James B. McNAIR 
In Rhus diversiloba T. and G. the resin passages are situated in 
the roots, stems, leaves, and fruit in the phloem of the primary 
vascular bundles. In addition, there are others in the secondary 
bast of the stem and root. 
The root contains a single wide resin canal in each of the phloem 
portions of the primary bast. In the secondary bast, resin canals 
in concentric circles with smaller lumina are successively added. 
After the secondary phloem is formed in the root, the xylem and 
phloem are formed exactly as in the stem. 
In the stem the phloem portion of the primary bundles is 
separated from the parenchymatous outer cortex by a strong bundle 
of sclerenchymatous (bast) fibers of crescent-shaped transverse 
section. These fibrous bundles are almost in contact with one 
another at their margins, and thus constitute a ring around the 
outer cortex. Outside of this sclerenchymatic ring no resin pas- 
sages are found, but large ones are located immediately within it, 
one in the phloem of each vascular bundle. In the secondary 
cortex, which, is formed later internally, new canals are formed 
successively in the strands of the bast. The cortical passages of 
the secondary bast are connected in the internodes by more or 
less numerous tangential anastomoses, and thus combine to form 
a more or less complete cylindrical network in the bark concentric 
with the stem cylinder. The cortical passages in the nodes 
anastomose with one another. The leaf passages extend up the 
internode to the plexus of anastomoses. 
The vascular bundles which pass into the petiole are arranged 
in curves to follow the outline of the petiole in its transverse sec- 
tion. These branch when they reach the leaflets. The resin pas- 
sages are arranged in the petiole as in the primary vascular bundles. 
The canals may be absent in the weaker bundles, however. 
In the midrib of the leaflets the fibrovascular system is divided 
into two parts. One, the superior, the ventral, is formed of 3 
Botanical Gazette, vol. 65] [268 
