146 OUTLINES OF PLANT LIFE. 



rinsed thoroughly in 5 per cent, formalin and again rinsed in water. 

 Cork or cover tightly. After 24-48 hours remove cover and thrust in a 

 burning match or candle attached to a wire. If COj has been produced 

 it will extinguish flame. Test also by lowering into jar a vessel of 

 baryta-water. If precipitate or film forms it shows presence of COj. 



Demonstration. — To show evolution of CC^ by respiration of leaves 

 and flowers. 



Provide a piece of plate glass and a , bell jar with ground rim, of suit- 

 able size to cover a blooming plant growing in a pot. Alongside the pot 

 place a shallow dish of baryta-water ; cover both with the bell, daubing 

 its edge with vaseline to make contact with glass plate air-tight. Place 

 in darkness. Note film of barium carbonate on surface of water after a 

 day. Conduct a control experiment, identical but for the absence of 

 plant. Is more or less barium carbonate formed ? Why darken ? 



200. Respiratory ratio. — The ratio between the amount 

 of oxygen consumed and carbon dioxid produced varies 

 somewhat with the age and condition of the plant, as well 

 as with the circumstances under which respiration occurs. 

 Ordinarily the volume of carbon dioxid produced is approx- 

 imately equal to the volume of oxygen consumed, and the 



ratio may be expressed thus : —r— = i. 



201. Respiration and photosynthesis. — In the green plants 

 respiration is masked in daylight by photosynthesis. When- 

 ever the green parts are sufficiently illuminated, the carbon 

 dioxid produced by their respiration is consumed in the 

 formation of food. But when these parts are not adequately 

 illuminated, the process of photosynthesis is interrupted, and 

 respiration can be more easily studied. The parts of plants 

 which are free from chlorophyll, such as young flowers, buds, 

 embryos, and the like, and all the non-green plants, allow 

 the respiratory changes to be demonstrated readily. 



202. Aeration. — The oxygen consumed comes from the 

 atmosphere, or from that dissolved in water. Certain plants 

 are adapted to aerial respiration, while others are adapted to 

 aquatic respiration, but in either case the gas used is the 



