370 Cooke and Schively on Observations on the 
ably only another of the degeneration effects due to para- 
sitism. 
In a section through a mature stem just above the tuber, 
the bundles form a quite regular narrow ring, its width 
being less than one-sixth the entire diameter of the stem. 
There were twenty-one separate bundles, varying greatly 
in size. There is an average size presented by about two- 
thirds of all the bundles. The remainder are mostly smaller, 
some being mere rudiments of bundles, less than one-twen- 
tieth the usual size. A few are larger than the average. 
Frequently two bundles are seen fused together. 
An individual bundle is wedge-shaped in section, taper- 
ing inward toward the pith. The outer area is formed of 
hard bast cells, and is the most extensive cell area in the 
entire bundle. It consists of cells with extremely thick 
rounded cell walls and devoid of intercellular spaces. The 
greater extent of the cell wall stains scarcely at all, and is 
clear and refractive. The outermost layer stains deeply 
with saffranin, looking like a fine red line passing around 
the cell. It forms sharp angles at the cell intersections, 
while the inner margin of the cell wall is perfectly round 
and smooth. 
Below these bast fibres lies the true phloem, nearly equal- 
ing them in amount. This region takes methyl green stain 
exclusively in saffranin anilin green double stain, and is 
characterized by protoplasmic, thin-walled delicate tissue. 
There are numerous large rounded phloem cells, and scat- 
tered among these are much smaller cells with a sharply 
angular outline. These cells invariably contain a dense, 
green-stained, balled-up mass. Their appearance is iden- 
tically that of sieve-tubes in section, yet I have not been 
able to assure myself of the presence of sieve-plates in the 
longitudinal sections. It may be that degeneration has 
caused the loss of these structures, while the cells that pos- 
sessed them remain. 
The xylem cells lie next within, and are chiefly notable 
