64 STUDY OF COMMON PLAJSTS. 



one or more of the leaves so as to exclude the light by 

 pinning flat pieces of cork closely on opposite sides. After 

 the plant has been in the light for a day or more, proper 

 tests show that starch has been formed in the parts of the 

 leaves exposed to light but is absent where they were 

 covered (except in the fibro-vascular bundles). Further 

 details are given by 'Detmer, Das pflamenphysiologische 

 Fraktikum, pp. 33-34 and 37-38. 



IV. Place an inverted funnel over a lot of Elodea, 

 growing in a glass jar, and push it down until the small 

 end of the funnel is beneath the surface of the water. 

 Fill a test-tube with water, stop it with the thumb, invert, 

 and (under water) bring the small end of the funnel into 

 it. Set the apparatus where it will be in bright sunlight. 

 Observe the bubbles of gas given off by the plant. After 

 enough has been collected in the tube, test for oxygen. 

 This may be done by lighting a match and blowing it out, 

 and then inserting it, while still glowing, into the test- 

 tube. 



V. The preceding observations show that starch is 

 formed in the chlorophyll bodies in the presence of sun- 

 light, and that during the process oxygen is given off. 

 By means of a simple experiment it may also be shown 

 that starch is not thus produced unless carbon dioxide is 

 supplied to the plant. The teacher will find the apparatus 

 figured and described by Detmer, Praktikum, p. 38, easily 

 made and entirely satisfactory. 



Transpiration. 



I. Take a quantity of green leaves and place them in a 

 wide-mouthed bottle. After a time observe the moisture 

 that has collected on its inner surface. Where has it 

 come from ? 



