80 PHOTOSYNTHESIS AND RESPIRATION. 



ordinary air. Press a glass funnel down on the plants, and either fit 

 a piece of rubber tubing to the tube of the funnel, or, better, invert 

 over the latter a test-tube filled with water, so as to collect the gas 

 given off by the plants. That this gas is oxygen (in reality, air rich 

 in oxygen) can easily be proved by its causing a glowing splinter of 

 wood to burst into flame, or by corking the end of the tube while 

 still in the water, transferring the tube to a vessel containing solution 

 of pyrogallol in caustic potash and opening it, when the gas will be 

 almost entirely absorbed by the solution ; see Art. 56 (c). 



* (c) Keep your water-plants in darkness until the leaves show little or 

 no starch, then transfer them to water which has been boiled (to expel 

 the dissolved gases) and then cooled. Expose them to light, with 

 funnel and test-tube as before. Is any oxygen given off by the plants, 

 and do they make any starch ? 



116. Which Farts of the Plant absorb Carbon 

 Dioxide? Are the leaves (or other green organs) alone 

 able to absorb and use the carbon dioxide of the atmo- 

 sphere ? 



* (a) Get five wide-mouthed bottles, with tightly fitting corks. Wash 

 each bottle out with water, to keep the air inside it moist, and label 

 each with a number (1 to 5). Leave 1 empty, to serve as a check or 

 " control." Into 2 and 3 put some living green leaves ; into 4, some 



green leaves which have been killed by boiling ; into 5, some pieces of 

 ving wood cut from a branch, or some roots, or mushrooms, or an}' 

 other living but not green tissue. Charge the bottles with carbon 

 dioxide by breathing into each several times. Another plan is to pour 

 into each jar some "plain soda-water" from a syphon (a convenient 

 method is to use a Sparklet syphon, charging it without adding soda) ; 

 the "soda-water" is of course simply water charged with carbon dioxide. 

 Cork each bottle tightly, smearing the edges of the corks with vaseline. 

 Place bottle 2 in the dark, the others in the light, for a whole day. 

 Then test each bottle for carbon dioxide by pouring in a little lime- 

 water and seeing whether it turns milky. 



Try the experiments several times, and record your results, with the 

 inferences to be drawn from them. If carefully carried out, these 

 experiments will show (1) that living green leaves absorb carbon dioxide 

 from the air in sunlight, (2) that they do not absorb it in darkness, (3) 

 that dead leaves do not absorb carbon dioxide, (4) that living but not 

 green parts of plants do not absorb it. 



* (b) Repeat the observations on the giving-off of oxygen by water- 

 plants, but put into the water, along with the water-plant, pieces of 

 living roots and of mushrooms. Do these living but not green tissues 

 give off oxygen ? If any gas-bubbles escape from them, do they come 

 off in light only, or in darkness as well ? 



