THE LEAF 
169 
a glass vessel full of water, and invert over it a glass funnel, or a long- 
necked bottle from which the bottom has been removed as directed in Exp. 
53. Expel the air from the neck of the funnel — 
or bottle—by submerging and corking under water 
so as to make it air-tight. Place in the sunlight and 
notice the bubbles that begin to rise from the cut 
end of the plant. When they have partly filled the 
neck of the funnel, remove the stopper and thrust 
in a glowing splinter. If it bursts into flame, or 
glows more brightly, what is the gas that was given 
off? (Exp. 22.) 
As oxygen is not a product of respiration, some 
other process must be at work here, during which 
oxygen is set free, and some other substance used 
up. (Exps. 24 and 25.) 
EXPERIMENT 67, WHATIS THE SUBSTANCE TAKEN 
IN WHEN OXYGEN IS GIVEN orr? — Fill two glass 
jars, or two tumblers, with water, to expel the 
air, and invert in a shallow dish of water, having 
first introduced a freshly cut sprig of some healthy 
green plant into one of them. Then, by means 
of a bent tube, blow into the mouth of each tumbler 
till all the water is expelled by the impure air 
from the lungs. Set the dish in the sunshine and 
leave it, taking care that the end of the cutting is in 
the water of the dish. After forty-eight hours re- 
move the tumblers by running under the mouth of 
Fig. 225. — Experi- 
ment showing that 
green plants give off 
oxygen in sunlight. 
each, before lifting from the dish, a piece of glass well coated with vaseline 
(lard will answer), and pressing it down tight so that no air can enter. 
Place the tumblers in an upright position, 
keeping them securely covered. Fasten a 
lighted taper or match to the end of a wire, 
plunge it quickly first into one tumbler, then 
into the other, and note the result. What 
was the gas blown from your lungs into the 
Fic. 226.— Experiment jars? (Exps. 23,24.) Why did the taper not 
for showing that leavesabsorb go out in the second jar? What had become 
carbon dioxide from the at- 
iOEphete. of the carbon dioxide? 
EXPERIMENT 68. To SHOW THAT LIGHT 
IS NECESSARY FOR A PLANT TO ABSORB CARBON DIOXIDE AND GIVE OFF 
OXYGEN. — Repeat Exp. 66, keeping the plant in a dark or shady place; 
do you see any bubbles? Test with a glowing match; is any oxygen 
