Structure, etc., of Epiphegus Virginiana. 373 
the pith. Frequently almost the entire central core of the 
tuber has cells showing this yellow-stained thickening, and 
sends out great radiating arms of such tissue through the 
bundle region, forming a star-like pattern. 
The xylem occurs in small areas of thickened cells, spiral 
and reticulated tracheids, no long trachea appearing. Scat- 
tered in among these tracheids are the peculiar large proto- 
plasmic cells that are associated in parasitic connection with 
the host, as will be shown later. 
The phloem cells stream outward and inward from the 
xylem in irregular masses and long radiating arms. The 
cells are small, angular and of two sizes. They stain deeply, 
seeming to be densely protoplasmic The smaller cells, the 
degenerate sieve-tubes, probably possess a stained nucleus 
lying next the side wall. In longitudinal section the phloem 
is seen to consist of remarkably small cells. They are both 
short, and extremely narrow and fine. They sometimes 
taper to a point, sometimes meet with flattened ends, which 
have each a thickened cap-like structure. This may be the 
remains of the sieve-passage between cells. External to each 
bundle there is usually a considerable development of the 
thickened brown-stained fibrous tissue or “hard bast.” 
The fundamental tissue of the tuber shows two well- 
marked regions. First, there is an area lying external to the 
outer bundles and the circle of hard bast. This area shows 
large circular cells with somewhat thickened walls, all tak- 
ing the brown stain. The cells are entirely empty, have 
neither nucleus, cytoplasm nor starch. The outermost cells 
are stretched out, often split apart and in process of slough- 
ing off. They have deeply stained thickened walls, and fre- 
quently show numerous large, oily-looking globules, a tan- 
nin precipitate probably. The inner area of the parenchyma 
lies within the hard-bast ring, and is sharply distinguished 
from the outer one in that its cells take on hematoxylin 
stain. The cells are large, thin-walled, irregular in out- 
line; they contain a pale brown-stained nucleus and nucle- 
