10 STUDIES IN ROOT-PARASITISM, 
meristematic activity in the distal end of the haustorium. There 
is less opportunity for the deposition of starch where the cells are 
in such active division, and the deposition of such starch indicates 
a tendency in the cells to cease dividing and become permanent. 
7. Shortly after the haustorium comes into contact with 
the root of a host, important changes take place in its tissues. 
An oval area of clear cells altogether free from starch appears 
among the radiating cells in the median line. This oval area is 
the first indication of the ‘‘nucleus” of the haustorium, the parts 
on either side forming the ‘“ cortex” (Plate IIT, fig. 2). It should 
be borne in mind that these terms are purely empirical and a 
matter of convenience. The regions so called do not correspond 
with definite portions of the mother root, nor are they homolo- 
gous altogether with the similar regions in the haustorium of 
Santalum. The term “nucleus” in any haustorium refers to that 
median portion which in early stages is differentiated by the 
character of its cell contents from the parts outside, undergoes 
rapid cell division and takes the chief part in the formation of 
the axis. It is probably only the lower part of the oval area now 
described which forms the nucleus in Olaz. 
The cortex of the haustorium is seen to consist partly of the 
outer permanent mantle of irregularly arranged cells already 
mentioned and partly of that portion of the radiating rows of 
cells of the last stage which are not included in the nucleus, but 
clothe it on either side. While thus the nucleus is employed in 
cell division and its cells are prevented from growing in length by 
the opposition of the host’s root, the cortical cells expand and 
grow along the outer side of the root attacked, forming the 
cortical or clasping folds which thus early help to fix the hausto- 
rium to the host. This takes place with a certain amount of force, 
as is evidenced by the burrowing action of the folds in the bark 
of the host (Plate ITI, fig. 2). 
The outer, irregularly arranged cells have become a perma- 
nent mantle round the tissues inside them, perforated at the 
proximal end by the strand of vessels from the mother root. 
