234 



NUTRITIVE METABOLISM 



the connections, fill the burette with mercury, or water, and draw 

 out a sample of air for analysis to determine exactly the propor- 

 tion of carbon dioxide present. Allow the bell-jar to remain 

 exposed to the light for three or four hours, then make a second 

 estimation. What proportion of this gas has been used in pho- 

 tosynthesis ? Repeat with 10 and 20 per cent, of the gas. 

 What is the result in both instances ? l 



300. Influence of Temperatures upon Photosynthesis. Set up 

 the experiment as in 301 using 10 per cent, of the gas and test 

 the amount used during a period of three 

 hours at a temperature of 20 C. Repeat and 

 place a large piece of ice in the bell-jar, or use 

 any method by which the temperature may 

 be reduced to 12-15° C. 



301. Influence of Various Portions of the 

 Spectrum upon Photosynthesis. Secure two 

 tall cylinders of a height of about 30 cm;, of a 

 diameter of about 8 and 12 cm. respectively. 

 Place a piece of lead or iron in the bottom of 

 the smaller one and set it inside the larger. 

 Fill the larger one with a liquid which will 

 permit only red rays to pass. Place a shoot 

 of any convenient plant inside the smaller 

 cylinder and fit it with the apparatus attached 

 to the bell-jar in 302. Run in enough car- 

 bon dioxide to make about five per cent, of 

 the enclosed air, close the cylinder tightly by 

 means of a large waxed cork stopper through 

 which the various tubes pass, and set in sun- 

 light for three hours. Make an estimation of the amount of 

 carbon dioxide present at the beginning and end of the test. 

 Repeat, using a solution in the outer cylinder which will permit 



1 See Schaible, F. Physiologische Experimente ueber das Wachstum und die 

 Keimung einiger Pflanzen unter verminderten Luftdruck. Beitr. z. Wiss. Bot. 4 : 

 94. 1900. 



Fig. 117. Two cylin- 

 ders arranged to expose 

 plant to light which has 

 passed through colored 

 solutions. c, large 

 cork, with perforations 

 for tubing, b, layer of 

 colored fluid. 



