CHAPTER XIII. 

 WORK OF LEAVES (Concluded). 



V. RESPIRATION. 



181. The leaves are also organs for respiration, but since 

 respiration takes place in all growing parts of plants the subject 

 will here be treated with reference to plants in general. 



182. How seedlings breathe. Plants breathe just as truly 

 as animals do, though they do not have lungs. Breathing, in 

 animals as in plants, is the taking in of a gas, oxygen, into the 

 body, and giving off, or excreting another kind of gas, carbon 

 dioxide. That germinating seeds give off carbon dioxide can be 

 shown in the following way. A quart of peas which have been 

 soaked in water for twelve or fifteen hours, are placed, without 

 any water, in two fruit jars or two large wide -mouthed bottles, 

 which are then closed tightly. Another jar or bottle empty but 

 closed tightly is kept as a check. In twenty-four hours let us 

 pour a small quantity of barium hydrate* down the inside of the 

 jar or bottle, and close the bottle quickly again. A white pre- 

 cipitate f is formed. If the bottle is opened again and tipped so 

 as to pour some of the gas into an open vessel with a little barium 

 hydrate, the white precipitate appears in the vessel of baryta 

 water. The gas is heavier than air and is easily poured into the 

 baryta water. If some of the barium hydrate is poured into the 

 empty bottle, no precipitate is formed or only a very small 

 quantity. 



Now in the other bottle the lighted end of a splinter or taper 

 may be lowered. The flame is immediately extinguished be- 



* To make barium hydrate. Dissolve barium oxide in water. 

 and keep in a tightly corked bottle, 

 f This is barium carbonate, BaCO 3 . 



108 



Filter 



