Dixon—Note on Supply of Water to Leaves on « Dead Branch. 11 
cause the fading by partially cutting off the water-supply. The pro- 
bability of this explanation is lessened by the fact that the decoction 
causes the fading even after it has been repeatedly filtered. In any 
ease the observation, taken along with the previous experiments, 
may be regarded as confirmatory of the view that the fading is 
largely due to the plasmolysing or poisonous effects of substances 
extracted from the dead cells. : 
The contaminated nature of the water supplied through a dead 
branch may be demonstrated by collecting some of the water 
transmitted through a branch killed by the application of hot 
water, asin the previous experiments. If Syringa vulgaris is used, 
the water transmitted is of a dark brown colour, and quite different 
in appearance from what is transmitted through a living branch 
under similar circumstances. If this brown fluid is supplied to 
eut transpiring branches, the latter rapidly fade and wither. When 
making this experiment, I killed the lower 30 cms. of a straight 
branch 40 cms. long, by immersion in hot water. The branch was 
then inverted and water forced through it under a head of 20 cms. 
The water transmitted was thus filtered through 10 cms. of living 
wood after its passage through the dead portion. After transmis- 
sion, it was twice filtered, and supplied to cut branches. These 
latter faded in two and a half days, while controls did not show 
signs of fading for several days later. 
The foregoing observations seem to me to show that the 
exudations from the dead cells are sufficient in themselves to cause 
the fading of the leaves above the killed portions of the stem. 
However, it also appears evident that if the leaves exerted much 
tension during the application of the high temperature, this 
tension might easily cause the rupture of the water-columns, while 
the tensile strength of the water was diminished owing to its 
increased vapour-pressure at the higher temperature. 
To investigate this possibility I endeavoured to arrange that 
the water in the conducting tracts should re-establish continuity 
after the withdrawal of the hot water. In order to do this, I 
removed an annular piece of the bark in the middle of the 
heated portion of the branch experimented upon. This annular 
incision laid bare the wood, and put its tubular elements in com- 
munication with the surrounding water. This water, which was 
applied boiling, was allowed to cool gradually. All this time the 
