PAA STUDIES IN ROOT-PARASITISM. 
This specimen is unusual in certain respects (due partly to 
the fact that the root entered is that of a monocotyledon) and 
therefore not altogether useful in the series, but it has the great 
advantage over the other sections obtained of forming a stepping 
stone between the younger gland-bearing stage and those which 
have penetrated and lost all signs of that organ, and, after a 
comparison with the stage shown on Plate VI, we are able to 
locate most of the tissues. The nuclear meristem has, indeed, 
changed almost out of all recognition, having thrust itself into 
the breach in the form of the sucker and swollen out there, 
besides developing a thick central strand of vessels. But, with 
the exception of the latter, the change in the tissues is chiefly 
such as would inevitably result from a great and sudden elonga- 
tion of all the cells. There are probably not many more cells 
in the nuclear region of Plate VII than in that of Plate VI. 
The cortical cells have taken small part in the great expansion 
which has led to the formation of the sucker, excepting perhaps 
on the two sides where a small portion may have been dragged 
in. This might be expected from the much more meristematic 
nature of the nuclear cells than those of the surrounding cortex, 
and the small cortical masses dragged in have no part in the 
activity of the sucker. We see in this a further difference 
between Olax and Santalum. In Olax the sucker is formed of the 
cells of the nucleus, while in Santalum the cortex takes a distinct 
share in its formation, accompanying the nuclear tissues on each 
side. This difference has its explanation in the destructive action 
of the gland in Olaz on all the tissues below it and at its sides. 
The great advantage of the section on Plate VII, however, 
over all others met with of a similar age is that, by a careful 
comparison with that on Plate VI, we can at once lay our finger 
on the zone of clear cells with the collapsed layers outside them. 
We see also that the collapsed layers are being extended upwards, 
but this region is irregular in the section and will be referred to 
in a later specimen. | 
The median vascular strand passes upwards into a horizontal 
band of vessels (already indicated in the two previous Plates), 
