CHAPTER X. 



THE RESPIRATION OF PLANTS. 



Living 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 living in 

 moist places, like the arum or water lily, have 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. 28. To show that Air Passages are Continuous Throughout 

 the Plant. — Partly fill a flask with water and provide it with a stopper 

 containing two holes. Into one insert the stem of a leafy 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 above 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. 29. 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 cover the stem for an inch or so. 

 Attach 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 

 find its way 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 bicycle pump to compress the air. This 

 experiment must be performed when the leaves are active ; in winter when 

 the leaves have fallen the lenticels are closed so that no air is admitted 

 and no water escapes through them. 



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