2320 



Journal of Applied Microscopy 



determine how long the shoot continues to bend in the same direction as before, 

 determine also the time when the shoot begins to retrace its path. 



Which of these two periods is the After Effect ? Which is the Latent Period 

 in this experiment ? How does it compare with the Latent Period in the pre- 

 ceding experiment ? 



4. Effect of Light Waves of Different Length. Prepare two jars of mustard 

 {Sinapis alba) or buckwheat {^Fagopynim esciilentiim) seedlings as in Experiment 

 1. Place one jar in a heliotropic chamber admitting only orange-colored light, 

 the other in a chamber admitting only blue light. 



Figure 16 shows a simple heliotropic chamber fitted with a chromatic win- 

 dow. The inner surface of the box is painted dead black, a tightly fitting door 

 is made on one side of the box and a small opening cut in one end. The chro- 



FiG. 16 — Heliotropic Chamber Fitted witii a Chromatic Window. 



matic window is made as follows : Select a large glass bottle with smooth 

 parallel sides, cut holes in the cover and bottom of a cigar box of such a size 

 that they will transmit no light except that which passes through the walls of the 

 bottle when it is placed inside of the box. Pack the bottle tightly in the cigar 

 box with black wadding and place it before the opening in the end of the cham- 

 ber. In order to obtain orange light, fill the bottle with a saturated aqueous 

 solution of potassium bichromate ; to obtain blue light, fill the bottle wath a 

 solution of ammoniacal copper sulphate. 



Observations should be made and the experiment ended within twenty-four 

 hours. The short blue waves of the spectrum will invariably produce the great- 

 est curves. Compare the results of this experiment with the light waves effec- 

 tive in carbon assimilation. Howard S. Reed. 



University of Michigan. 



