2 STUDIES IN ROOT-PARASITISM. 
a 
the cortex right to the centre of the nuclear area, and it is diffi- 
cult to draw any sharp distinction between cortical and nuclear 
regions where they pass into one another. The radial arrange- 
ment of the cells becomes gradually obscured in the nucleus by 
the rapid divisions taking place, while the cortex, as a whole, 
retains a radial arrangement for almost its entire existence (see 
paragraph 16). 
8. It has been found difficult in the sections available to 
trace the stage just considered further, so much so that one is 
tempted to suggest two independent lines of development in Olaa 
haustoria. The stage next met with shows sharp constriction at 
the top of the oval area and its consequent division into an 
upper and lower part. Two cases have, it is true, been met with 
where such a constriction may be thought to be actually taking 
place by the filling of a small triangular mass of cells on each side 
with starch grains, and thus simulating an ingrowth of the 
cortex, but the sections are not always very convincing. We shall 
assume that fig. | on Plate IV is the next stage in development, 
and that the small triangular areas ¢ ¢ divide the meristematic 
area into two parts. 
The separation of nucleus proper from the vascular loop is 
well seen on Plates I1V—VI. Leaving the vascular loop, which 
is usually quite immature, alone for the present, we find a series 
of remarkable changes taking place in the nucleus and cortex. 
The nucleus as a whole remains meristematic and unaltered save 
for the massing of plastic materials in its cells, but the gland 
develops rapidly, and largely at its expense. This organ has 
become sharply marked out as an oval region inside the nucleus, 
at first surrounded on all sides by protoplasmic cells (figs. 1—3), 
but, later on, growing to such a size and taking up so much for 
the nuclear space that it is not possible to say whether any 
of the latter tissue remains outside it excepting at the proximal 
end (fig. 4). 
A great change has also taken place in the arrangement of 
the starchy and clear cells of the cortex. While the gland is 
