12 Scientific Proceedings, Royal Dublin Society. 
leaves above were wrapped in a damp cloth to reduce evaporation 
from them to a minimum, and, with it, the tensile stress in the 
conduits. As the water surrounding the branch cooled, continuity 
was presumably re-established in most of the ruptured water- 
columns. The leaves treated in this way did not retain their 
turgidity appreciably longer than those on branches not ringed, 
but otherwise similarly treated. Sometimes a small delay in the 
fading of these ringed branches was noticed; but this might be 
explained by the dilution, introduced through the ring, of the 
substances exuded by the dead cells. ; 
The experiment, however, cannot be regarded as satisfactory, 
as it is by no means proved that continuity is re-established in a 
sufficient number of capillary tracts in order that an adequate 
quantity of water may be supplied to the leaves, and consequently 
we cannot be certain what would happen if continuity were 
thoroughly re-established. Furthermore, the fading in this 
exper.ment cannot be regarded as exclusively caused by rupture, 
inasmuch as other causes are allowed to act. 
CoNCLUSIONS. 
The considerations mentioned in this note seem to indicate 
phate 
1. It is unnecessary to attribute to the cells of the stem a 
special function in the elevation of water, because the leaves above 
fade when these cells are killed by heat. 
2. The fading of the leaves in these cases is probably largely 
due to the introduction of poisonous or plasmolysing substances 
into the leaves from the dead cells. 
3. Clogging due to the exudation of comparatively imperme- 
able substances into the water-conducting tissues of the plant may 
also contribute to the fading of the leaves. 
4, It is further possible that the application of heat in these 
experiments may permanently interrupt the water-supply by 
breaking the water-columns, on the continuity of which the water- 
supply depends. 
