34 Gardening 
2. Fo show that a leaf gives off water. Draw the stem of a 
healthy young leaf (cabbage or geranium will do) through a hole 
in a square of cardboard. Seal about the stem of the leaf with 
Fics. 25, 26, and 27. Experiments to show that leaves give off water. 
paraffin heated only to the melting point (too hot paraffin will 
kill the stem of the leaf and spoil the experiment). Then arrange 
the experiment as in Figure 25, making sure that the upper drink- 
ing glass fits snugly to the cardboard. 
Arrange two other glasses in the same manner but make no 
hole in the cardboard and omit the leaf. Set both pairs of glasses 
in the sunlight for several hours. 
Where does the water come from that collects in the glass 
inclosing the leaf? What happens to a leaf if it is not supplied 
with water? 
The second pair of glasses is used as a “check” or “control”’ 
in the experiment. Why is it advisable to have a check in experi- 
mental work ? 
That a plant gives off water can be shown also in the manner 
indicated in Figures 26 and 27. When the experiment is carried 
out as suggested in Figure 26, the twig is left attached to the tree. 
When done as indicated in Figure 27, the leaves should be placed 
in the sun. 
Transpiration may be demonstrated also by turning a large glass 
vessel over a potted plant, after the pot has been wrapped in sheet 
