WORK OF THE SHOOT 



79 



Photosynthesis 



Carbon as a plant food. Photosynthesis. Take a series 

 of jars (1-5) similar to that shown in Fig. 49. In (1) place 

 a little water and charge the bottle with sufficient carbon 

 dioxide to extinguish a taper. Put in this one or two 

 green leaves and close securely ; then expose to bright 

 sunlight. Prepare the other bottles in the same way, but 

 in (2) place leaves that have been killed by boiling ; in (3) 



Fig. 49. Experiment to 

 show that Green Leaves 

 exposed to Sunlight absorb 

 Carbon Dioxide. 



Fig. 50. Experiment to 

 show that Shoots of Water- 

 weed exposed to Sunlight 

 give off Oxygen. 



living non-green roots ; in (4) carbon dioxide only, as 

 a control, and in (5) the same as in (1), but let this be kept 

 in the dark while the others are exposed to sunlight. 



Leave these for a day or two, then test each (a) with 

 a lighted taper for oxygen and (b) with lime-water for 

 carbon dioxide. Under what conditions has carbon 

 dioxide disappeared and oxygen taken its place ? 



From this experiment we learn that green leaves under 

 the influence of sunlight are able to take up carbon dioxide 



