Cannon : Anatomy of Phoradendron villosum Nutt. 383 



sure. It is not likely that the sinker absorbs the adjacent tissue of 

 the host to any extent because no evidence of this was seen, and, 

 further, there is an absence of epithelial cells, or of cells having 

 that general character, in the sinker. The cells of the young 

 sinker which correspond in position to epithelial cells of the corti- 

 cal haustoria are cubical, and thick-walled. No cells in mature 

 sinkers exhibit epithelial characters ; the change in structure and 

 in function of these cells takes place in the meristematic region of 

 the host. 



A cross section of an oak branch to which a mistletoe is at- 

 tached shows that the sinkers of the parasite take the position of 

 the host's medullary rays, and that the structure of portions of the 

 sinker varies according to their relative positions. The part of the 

 sinker which is in the cortex of the host agrees very well in struc- 

 ture with the cortical haustoria, but that portion which is within the 

 xylem has a different and a characteristic structure. The sinker 

 taken as a whole is composed of a central cylinder and a surround- 



« 



ing cortex. The central cylinder is, in both portions of the sinker, 

 an almost uniform structure, but the cortex is variable. The cor- 

 tex of that part of the sinker that is within the cortex of the host 

 is composed of thin-walled cells and has few intercellular spaces. 

 On the other hand, the outer part of the sinker cortex, which is 

 within the wood cylinder of the host, has a denser structure, and 

 is made up of heavy-walled cells with no intercellular spaces. 

 The inner portion of the same part of the cortex is composed of 

 thin-walled cells between which there are small spaces. Between 

 the two sorts of sinker cortex just spoken of, and in a position 

 approximately adjacent to the host cambium is the meristematic 

 portion. Here the cells are brick-shaped, relatively small, and 

 there are no intercellular spaces. The contents of the sinker cells 

 appear to be almost entirely composed of starch in character re- 

 sembling that of the cortical haustoria. The cells of the sinker 

 cortex remain alive in the oldest material that I examined, and 

 they probably die only as the parts of the host adjacent to them 

 die. The walls of all of the sinker cells which are within the cor- 

 tex of the host are lignified. 



The conductive tissue of the sinker is composed of a few spiral 

 and annular ducts which are enclosed by narrow, elongated thin- 



