30 



PRACTICAL COURSE IN BOTANY 



Let us see what became of it. Hold a lighted candle under the open end 

 of a test tube, or under the mouth of a small glass jar. Does any vapor 

 collect on the inside? After two or three minutes quickly invert the jar 

 or the tube, and thrust in a lighted match: what happens? Can the 

 substance now in the jar be ordinary air? Why not? (Exps. 21, 22.) 

 Pour in a small quantity of limewater, holding your hand over the mouth 

 of the tube to prevent the air from getting in ; the gas inside, being heavier 

 than air, will not escape immediately unless agitated. What change do 

 you notice in the limewater ? 



It has been proved by experiment that the kind of gas formed by the 

 burning candle has the property of turning limewater milky; hence, 

 whenever you see this effect produced in limewater, you may conclude 

 that this gas, known as carbon dioxide, is present ; and conversely, the 

 presence of carbon dioxide, especially if accompanied by some of the other 

 effects observed, as the giving out of heat and moisture, may be taken as 

 evidence that some process similar to that going on in the burning candle 

 is, or has been, at work. 



EXPERIMENT 24. Do THESE EFFECTS ACCOMPANY ANY OF THE LIFE 

 PROCESSES OF ANIMALS ? Blow your breath against the palm of your 

 hand ; what sensation do you feel ? Blow it against a mirror, or a piece 

 of common glass ; what do you see ? Blow through a 

 tube into the bottom of a glass containing limewater ; 

 how is the water affected ? How do these facts cor- 

 * respond with the results of Exp. 23 ? 



EXPERIMENT 25. Is THERE ANY EVIDENCE THAT 



A SIMILAR PROCESS GOES ON IN PLANTS ? (1) Half fill 



a small, wide-mouthed jar with limewater, place it in- 

 side a larger one (Fig. 46), and fill the space between 

 them, up to the neck of the smaller vessel, with well- 

 soaked peas, beans, or barleycorns, on a bed of moist 

 cotton or blotting paper. Cover with a piece of glass 

 and keep at a moderately warm temperature. (2) As 

 a control experiment, place beside this another jar ar- 

 ranged in precisely the same way, except that seeds 

 must be used whose vitality has been destroyed by 

 heat. To prevent the entrance of germs among the 

 dead seeds, which might cause fermentation and thus 



interfere with the experiment, set the jar containing them in a vessel of 



water and boil an hour or two before the experiment begins. Otherwise, 



treat precisely as in (1). 



After germination has taken place in (1), what change do you notice in 



the limewater ? If the effect is not apparent, gently stir with a straw or 



FIG. 46. Dia- 

 grammatic section, 

 showing arrange- 

 ment of jars for 

 Exp. 25. 



