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 re weighing 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? 



1 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. 



