78 



PHOTOSYNTHESIS AND RESPIRATION. 



carbon dioxide is given off, causing a white precipitate, when these 

 substances are strongly heated. These experiments show that all 

 parts of plants contain carbon, and that starch (the formation of 

 which in plants has been proved in the preceding experiments) also 

 contains carbon. 



* (b) Put a "Nasturtium" (Tropaeolum) leaf in a small bottle con- 

 taining water, so that its stalk dips well into the water while its blade 

 rests on the neck of the bottle. Pour some caustic potash into a wide- 

 necked glass jar, and lower the bottle with the leaf into this jar ; then 

 cork the jar tightly, and smear the edges of the cork with vaseline. 

 The leaf should be taken from a plant which has previously been kept 

 in darkness for two days. The leaf is now exposed to air whose carbon 

 dioxide is absorbed by the potash solution. Set up a control experi- 

 ment in which the arrangements are the same, but leave the jar open 

 or cover it with a cork (or a piece of wood) in which a hole is bored to 

 admit air. 



* (c) Use the same apparatus, but, instead of pouring caustic potash 

 into the jar, pass through a hole in the cork closing the jar the tube of 

 a funnel which is filled with soda-lime, or with lumps of caustic potash. 

 This will admit air, but absorb the carbon dioxide it contains. As a 

 control, use a similar apparatus, but place in the funnel gravel instead 

 of soda-lime or potash. 



Pig. 35. Moll's Experiment 



* (d) Fit a wide-mouthed bottle with a cork cut in two across the 

 middle. Smear with vaseline the edges of each half of the cork ; pour 

 some clear lime-water into the bottle. Then lay the bottle on its 

 side and place between the halves of the cork a Primrose leaf of con- 

 venient size, so that half the leaf is inside the bottle and the other 

 half outside (Fig. 35). The base of the leaf, outside of the bottle, 

 should dip into water in a small dish. See that the halves of the 

 cork are securely sealed with vaseline, then cover the whole apparatus 

 with a large bell- jar, and set it in a good light. After some hours, 

 remove the leaf, decolorise, and test with iodine. If the experiment 



