HOW THE ROOT LIFTS WATER 93 
through the potato tube. Does the water rise in this 
tube above the line of the water in the vessel outside ? 
Why? 
Nore. —-A living leaf of a plant may take the place of the bladder 
membrane. In the experiment illustrated in Fig. 129 the leaf of 
the cultivated nasturtium (Tropceolum) may be used instead of 
the bladder membrane. It is necessary to select a leaf which is free 
from any puncture, and it must be tied on carefully with a soft cord. 
In this experiment the sugar solution rose two or three inches in a day, 
and then rose no further. The thistle tube was then carefully lifted 
out, and the leaf was allowed to come in contact with boiling water to 
kill it. The tube was then replaced in the bottle of water. Strange 
as it may seem, the dead leaf worked much better as a membrane than 
the living leaf, and the sugar solution rose to near the top of the tube 
in two or three days. 
