EXERCISE 23 

 IS AIR NECESSARY FOR PHOTOSYNTHESIS? 



Materials. Plants; vaseline; benzine or gasoline; water bath; 

 beaker; alcohol; iodine. 



Directions for work. Air may be excluded from a leaf by 

 covering the stomata with such a substance as vaseline. Select 

 a plant which has been in the dark since the previous day. 

 Rub vaseline over the surfaces of several leaves, being particu- 

 larly careful to completely cover the lower surfaces. Place the 

 plant in bright sunshine for several hours. 



When the leaves have been exposed to the light long enough 

 to have accumulated considerable starch, remove the vaselined 

 leaves and several unvaselined leaves from the plant. Dissolve 

 off the vaseline with benzine. Remove chlorophyll and test for 

 starch. 



Compare the vaselined leaves with the unvaselined leaves, 

 noting the differences. What do these differences mean ? What 

 is your conclusion about the necessity of air for photosynthesis? 



NOTE. Air is composed of several gases. This experiment does not 

 attempt to show what part of the air is necessary for photosynthesis. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 13-17. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 34-39. 

 CALDWELL and EIKENBERRY. Elements of General Science, pp. 65, 

 66. Ginn and Company. 



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