130 RELATIONS OF PLANTS TO LIGHT 



197. Transmission of Stimulus-effects. If the cylinder of tin- 

 foil employed in the latter portion of the above experiment should 

 cover all the seedling except the extreme tip it would be found 

 that a reaction curvature would take place in a portion not di- 

 rectly exposed to the action of light, demonstrating that a trans- 

 mission of the effects of the stimulus has taken place. Trans- 

 mission toward the tip from a basal portion of a shoot has not 

 yet been observed. It has been found that transmission takes 

 place through the living parenchyma cells of the fundamental 

 tissues. 



198. Transmission in Stems. Strip a plant of Coleus of all of 

 its leaves and place it in a dark room for a day. Cover all of the 



stem except the apical internode with tinfoil, or pile 

 sphagnum around it and bind with rafia fiber to 

 effect the same purpose. Place the preparation in 

 a phototropic chamber, or in an open room where 

 it will be illuminated from one side only. Note the 

 position of the stem a day later. 1 



199. Rays Inducing Phototropic Reactions. Place 

 six seedlings of any of the species used in the pre- 

 vious experiments in the phototropic chamber and 

 put a flask with parallel walls in the receptacle in 

 the door. Fill the flask with an ammoniacal solu- 

 tion of copper oxide. This solution may be pre- 

 FIG. 66. Stem p ar d by adding an excess of ammonia to a watery 

 hototro ic7n so ^ ut i n f copper sulphate, and should be of such 

 after exposure concentration that a printed page may be read 

 of the termi- through the flask containing it. Set the ap- 

 paratus where a strong light may be thrown into 

 the chamber passing through the solution in the 

 flask. Examine six hours later, and note the angle of curva- 

 ture. 



Replace the seedlings with a second lot and refill the flask with 



a saturated solution of potassium bichromate in water. Note the 



1 Rothert, W. Ueber Heliotropismus. Cohn's Beitr. z. Biol. d. Pflanze, 7:1. 1896, 



