28 A LABORATORY MANYAL OF BOTANY 
posure relative to their bulk in order to prevent excessive 
drying? What advantages in having such plants develop 
water-storage tissue? What plants illustrate these points? 
LESSON XII 
Relation of plants to water—transpiration 
Materials.— Potted sunflower or geranium plants. 
Observation and study.—l. Experiment to show the 
exact amount of water used in a day by a plant. 
Select a thrifty plant. Over the top of the soil place a 
piece of sheet cork or sheet lead, cutting it so that it may 
be placed around the plant-stalk. Cut a small hole in this 
covering, and insert the lower end of a funnel-tube or this- 
tle-tube; with sealing-wax completely seal over and around 
the covering so as to prevent all evaporation from the soil. 
Allow the plant to stand until it needs water, then pour 
water into the thistle-tube and tabulate the amount used 
each day. See if the same is used when the plant stands in 
bright light as when it stands in shade. Is as much used at 
night as in daytime? Explain why. Cover the plant with a 
paper cone and see whether it uses as much water. Explain. 
2. Experiment to show whether leaves take up water as 
well as transpire it. 
Select three plants which have been allowed to become 
well wilted. Around the stalk of one and over the earth 
in the pot place some sheet rubber, so that no water can 
reach the earth. Then sprinkle the leaves thoroughly. In- 
vert the second, immerse the leaves in water, and secure the 
plant in this position for some time. Pour plenty of water 
upon the earth in the pot of the third plant. Note in each 
case whether the plants regain their normal condition, and 
state in the notes what is demonstrated by each plant. 
