Fes. 1909. | BOTANICAL SOCIETY OF EDINBURGH 29 
rich in reserve nitrogenous matter and without starch. As 
the structures just described abut on the vasa, they were 
able to draw water thence, store it for a time, and then 
pass it on to the thirsty cells around them. 
In the Bromeliaceee the roots frequently show swellings 
near the tip. But in general the effects of the attack of 
Heterodera can best be seen in fusiform enlargements 
some distance back. ‘These are inconspicuous until they 
have split open.' 
Rupture often takes place in the line of their long axis. 
The cortex is pierced. Sometimes even the vasa of the 
central cylinder are laid bare. Occasionally, with a lens, 
white specks in the innermost recesses of the fissure can 
be detected. These are, of course, the 2 Heterodera swollen 
with eggs. 
Now, because of the structure of the normal root, these 
ruptures, setting aside the» hypothesis of some mechanical 
disturbance, challenged investigation. In the Bromeliacez 
the root cortex shows in its middle a sheath of exceed- 
ingly hard sclerenchyma (Plate V. fig. 1). Section 
cutting is often a matter of great difficulty. But wher- 
ever these white specks could be made out, the sheath 
had evidently been pierced by some agent. Transverse 
sections showed an even more remarkable state of affairs, 
viz. that the sheath appeared never to have formed at 
the spots referred to. On one side of the section the 
thickened libriform sclerenchyma was replaced by a mass 
of thin-walled cells. 
The following is a general account of the changes 
observed :— 
In some extreme cases the whole of the central cylinder 
with the inner cortex had perished. The root was reduced 
to a sheath of sclerenchyma surrounded by the dried 
remains of the outer cortex. Occasionally traces of the 
piliferous layer could be distinguished. More often every 
indication of it had vanished. 
Where the destructive process had not gone so far the 
surviving tissues showed more or less disorganisation. 
1 The swellings at the tip have been investigated without, however, 
yielding any data that cannot better be taken from the second point of 
attack. 
