How Plants Live 35 
rubber or oilcloth fitted closely about the stem to prevent evapo- 
ration from the soil, The amount of water evaporated by a 
potted plant in a day can be determined by wrapping the pot as 
described above, weighing the pot and plant, and reweighing at 
the end of 24 hours. 
3. To show that plants respire. Soak 50 seeds of the garden 
pea in water for 24 hours. Then place them in a drinking glass 
with strips of wet blotting paper intermingled. As soon as the 
roots protrude, the young plants are ready for use. Secure two 
wide-mouth bottles of one-half-pint size with corks to fit tightly, 
and two small vials or wide-mouth bottles that can be placed within 
the larger bottles. Buy some limewater or make it.1 Place 25 
germinating seeds in one bottle, together with wet pieces of 
blotting paper; then place an open vial or small bottle nearly 
filled with limewater among the seeds. Cork securely. Prepare 
the other bottle in the same way but omit the seeds; this is the 
“check”? by which we can measure the action in the first bottle. 
Place the two bottles side by side in a warm room. 
Observe frequently for a period of 48 hours. Note that the 
surface of the limewater in the vial containing the seeds becomes 
coated with a white layer, and that this does not appear in the 
other vial. This white material is lime carbonate, formed by 
the chemical union of lime dissolved in the water and carbon 
dioxid in the air of the larger bottle. Where does the carbon 
dioxid come from? Why is it that no carbonate forms on the 
limewater in the check bottle? 
Now remove the cork from the bottle with the seeds and insert 
the burning end of a splinter of wood. Why does the flame 
immediately go out? Test the air in the other bottle in the same 
way. Why does the flame continue to burn? What do the 
growing pea plants remove from the air, and what do they give 
off into the air? 
‘ Crush a large lump of unslaked lime. Pour enough of this pul- 
verized lime into a bottle to fill it about one-third full. Then add 
twice as much water as lime. Cork the bottle and shake vigorously. 
Set aside for 24 hours; then pour off the clear water, being careful not 
to disturb the lime at the bottom. Filter this water through a fine 
cloth or filter paper, and keep it in a tightly corked bottle. 
