124 



RELATIONS OF PLANTS TO LIGHT 



that has passed through the solution with the solar spectrum. 

 Note the presence of several bars or bands (black or dark) cross- 

 ing the spectrum. Adjust the width of the slit 

 and the dispersion until these are seen most 

 distinctly. If an Abbe spectroscope is used 

 set the scale so that "75 " marks the lower 

 edge of the red color. Draw a similar scale 

 on a sheet of paper and plot the absorption 

 bands seven in number. Probably not more 

 than three or four may be seen simultaneously. 

 Repeat with other bottles containing layers of 

 fluid of different thicknesses. Also vary the 

 concentration of the solutions, and all may be 

 finally made out. Very satisfactory results 

 may also be obtained from the use of a direct 

 spectroscope of the pattern supplied to physical 

 laboratories. 



190. Action of Light on Chlorophyl Solutions. 

 Extract the chlorophyl from boiled leaves by 

 means of sulphuric ether instead of alcohol. 

 Secure an alcoholic solution of equal depth of 

 color. Divide both solutions into two lots 

 and thus fill four test-tubes. Place one each 

 of the alcoholic and ether solutions in a dark 

 chamber for a day, and the others in a strong 

 light. Compare the action of the light in the 

 two solutions and note the difference in color of 

 the solutions kept in the dark and in the light. 

 Fill four test-tubes with alcoholic solution and cork two of them 

 tightly. Expose and open closed tube in light and darkness. If 

 double-walled bell-jars or the apparatus in fig. 62 is used, a test 

 may be made of the influence of red and blue light in producing 

 this deterioration. The temperatures set up, however, are 

 such that the experiment is of but little final value (See color 

 filters). 



Fig. 62. Appa- 

 ratus for exposing 

 plants to separate por- 

 tions of spectrum. A, 

 glass cylinder fitted 

 with perforated stop- 

 per, and weighted 

 with lead, placed in a 

 larger cylinder. Col- 

 ored fluid is poured 

 in the outer cylinder 

 until it rises to the 

 level of the stopper 

 and a cover of tinted 

 glass is laid over the 

 whole (see color fil- 

 ters). 



