132 SOUTH AFRICAN BOTANY 
uncovered leaf. It will be found to be considerably 
less, thus showing that transpiration takes place through 
the stomata, since when they are blocked by vaseline it 
almost ceases. 
100. Experiment 10.—To demonstrate the sucking 
force exerted by leaves. 
Fe 
Fia. 73.-—-Apparatus by which Fic. 74.—Apparatus to Show the 
to Measure the Rate of Sucking Force Exerted by Leaves. 
Transpivation. 
Apparatus.—Glass and rubber tubing, mercury, small 
dish, stand branch. 
Method.—Obtain a branch with fresh young leaves 
and a fairly thick round stem. Cut the end under 
water, and keeping it under water attach to it a short 
piece of rubber tubing, and a piece of glass tubing. 
Tie the rubber tightly with thread or copper wire, and 
lift the whole apparatus out of the water. If it is air- 
