Structure, etc., of Epiphegus Virginiana. 373 



the pith. Frequently ahnost 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- 



