64 TRANSPIRATION AND ASCENT OF SAP ch. 



short time. This decoction, after repeated filtering, is 

 supplied to cut branches of the same tree. It will be found 

 that the leaves of the branches supplied with the decoction 

 fade and wither much more rapidly than those of con- 

 trol-branches supplied with water. For example, three 

 branches of Syringa vulgaris, set in a decoction of the 

 stem of the same plant, lost their turgidity within two 

 days, while the leaves of three control-branches were still 

 fresh after five days. 



Taken alone, this last observation would not be sufficient 

 to prove that in intact branches the withering of the leaves 

 is due to deleterious substances emerging from the killed 

 cells ; for it might be urged that colloid substances in the 

 decoction aggregating on the cut surface obstruct the free 

 transmission of water, and thus cause the fading by partially 

 cutting off the water-supply. The probability of this ex- 

 planation is lessened by the fact that the decoction causes 

 the fading even after it has been repeatedly filtered. In 

 any case 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 poison- 

 ous 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, as in the previous experiments. 

 If Syringa vulgaris is used, the water is of a dark 

 brown colour, and quite different in appearance from 

 what is transmitted through a living branch in similar 

 circumstances. If this brown fluid is supplied to cut trans- 

 piring branches, the latter rapidly fade and wither. When 

 making this experiment, I killed the lower 30 cm. of a 

 straight branch 40 cm. long, by immersion in hot water. 

 The branch was then inverted and water forced through 

 it under a head of 20 cm. The water transmitted was 

 thus filtered through 10 cm. of living wood after its passage 



