THE BREATHING OF THE PLANT 



77 



Fig. 37 



order to demonstrate its absorptive power a small 

 quantity of the acid, dissolved in water, may be put into 

 a well-corked bottle and left for a few hours ; then, by 

 the extinction of a lighted taper which 

 is thrust into the bottle, the absence of 

 oxygen is' proved. 



Two healthy bean-seedlings are sus- 

 pended, by means of cotton, in two bottles ; 

 at the bottom of one bottle is a solution 

 of pyrogallic acid ; in the other an equal 

 volume of water. The seedlings must not 

 touch the liquids. The bottles are then 

 well corked (Fig. 37). 



Observations. — The seedling which is 

 suspended over the water continues to 

 grow, while the one placed in the bottle containing 

 pyrogallic acid very soon dies. 



Inference. — A plant cannot live if deprived of oxygen. 

 In other words, a plant dies if it is unable to breathe. 



{Note. — In the case of the seedling that was suspended 

 over pyrogallic acid, a little further growth is observed 

 before the seedling begins to wither. This is due to 

 the fact that the oxygen contained within the seedling 

 itself is being used up in its respiration 

 (page 75). 



Experiment 49 



Aim. — To find out whether the breath- 

 ing of plants affects the temperature of 

 the surrounding air. 



Method. — A glass funnel is filled with 

 peas that have been soaked for two days 

 and are just beginning to germinate. The 

 funnel is then supported in a tumbler at 

 the bottom of which is a little water. A 

 bell-jar is placed over the whole. The 

 bell-jar is fitted with a one-holed cork, 

 and a thermometer is passed through the hole so that 

 its bulb dips down into the peas (Fig. 38). 



^^^ 



Fig. 38 



