CHvVPTER X, 



THE RESPIRATION OF PLANTS. 



LlviNC. things, plants as well as animals, respire both night and 

 day. All parts of a plant must be supplied with air for this 

 process. 



If the soil of an orange grove is not well drained or if it is 

 so compact that the roots do not get enough air, the trees look 

 yellow and unhealthy. The farmer restores trees to health by 

 removing the soil and exposing the roots. Plants lix'ing in 

 moist places, like the arum or water lily, ha\e large air chambers 

 running through the stem which supply air to the roots. The 

 hollow stems of the Pumpkins admit air to the part underneath 

 the large leaves. 



Ex. _'S. To show that Air Passages are Continuous Throughout 



the Plant. —l'*ai'th- till .\ flask with water and pro\'icle it with a stopper 

 containing two hole.s. Into one insert the stem of a leaf}' plant, into 

 the other a glass tube. The cut end of the stem should dip into the water. 

 By placing your mouth over the end of the tube remove the air from the 

 space abo\'e the water. Bubbles of air will rush from the cut end of the 

 stem. The air enters the plant through the stomata. If a water tap is 

 available an aspirator may be used to withdraw the air. 



Ex. 2g. Insert a woody stem of a Poplar (or some stem on which 

 lenticels can be seen) through the stopper of a flask, seal the lower end 

 with wax, and let the water of the flask cov^r the stem for an inch or so. 

 Att.ich an S-.shaped tube to the upper end of the stem by means of a piece 

 of rubber tubing. Pour mercury into the S-tube ; the compressed air will 

 lind its w■a^■ out through the lentice's into the water below.' 



A little over three-fourths of the air (seventy-seven parts) 

 consists of the gas nitrogen (N) ; about one-fifth is oxygen gas 



' Prof. Osterhout uses a bic\'cle pump to compress the air. This 

 experiment must be performed when the lea\'es are active ; in winter when 

 the lea\'es have fallen the lenticels are closed so that no air is admitted 

 and no water escapes through them. 



S3 6* 



