Water in Trees under Australian Conditions. 103 
(b) Stems killed by injecting with mercuric chloride and then saturated 
with water by means of high-pressure pump. 
(i) In dry air. 
J. 1^ hours 
3-2 cm. 
2. i| hours 
4 cm. 
(ii) In saturated atmosphere. 
1. 1^ hours 
2-4 cm. 
2. ii hours 
• 8 cm. 
The rate of ascent decreases in geometric progression as the 
experiment progresses and the liquid rises in the stem, as can be seen 
from the following and preceding data :— 
Nerimn Oleander. 
(a) Saturated stem in dry atmosphere: 
Duration of exp. Rate of ascent per hour. 
1. 3 hours 7*6 cm. 
2. 7 hours 4-3 cm. 
(b) Saturated stem in saturated atmosphere: 
1. 24 hours *42 cm. 
2. 4 hours 1.1 cm. 
3. 4 hours 1-2 cm. 
(e) Saturated stem killed with mercuric chloride in saturated atmo¬ 
sphere : 
1. 4 hours «4 cm. 
2. 24 hours -3 cm. 
Although the results show a certain amount of variation, they agree in 
so far as the most rapid ascent occurs in cut saturated branches in dry air, 
a less rapid ascent in a saturated atmosphere, and still less in the case of 
stems killed by means of mercury chloride. At first sight we have what 
seems a conclusive proof of an upward pumping action exerted by living 
stems, for it is difficult to see how any ascent could be produced by 
capillarity and evaporation in a saturated stem in a saturated atmosphere. 
The action does not seem, however, to be appreciably influenced by whether 
the stem is in the normal or inverted position provided both ends are equal 
in diameter, and further the fact that any rise at all is shown in a dead 
saturated stem in a saturated atmosphere is sufficient proof that the 
ascent is physical in origin. Its exact nature needs, however, further 
investigation. An ascent of liquid in a saturated stem in a saturated 
atmosphere at a rate of 12-15 cm. in an hour is too rapid to be explained 
by ordinary diffusion or imbibition. 
The rate of ascent decreases in geometric progression as the experi¬ 
ment progresses and the sap rises up the cut stem. Exactly the same 
applies to the capillary ascent in a glass tube, for, as the column rises, less 
and less force is available to overcome the gravitational acceleration and 
