MOVEMENT IN PLANTS. 223 



283. Dark Chamber for Fhototropism Experi- 

 ments. Make a " phototropic chamber," large enough to 

 contain pot plants. 



(a) Get a box of wood or stout cardboard, with one 

 side open ; the size should be about 40 X 40 X 20 cm. 

 Insert a vertical partition to divide the box into two equal 

 compartments (each 20 cm. square and 40 cm. high) ; 

 paint the whole of the inside black. The amount and 

 direction of the light falling on the plants can be further 

 regulated by placing over the open side a sheet of white 

 paper (for diffuse light), or a sheet of black paper or 

 cloth or card with a vertical slit cut out of it. 



(b) For various experiments, all that is required is a 

 cardboard box painted black inside and with a vertical slit 

 cut in one side (the side which is to face the light). Set 

 the pot of seedlings on a plate or shallow box of wet sand, 

 and let the rim of the dark-box rest on the sand so as to 

 exclude light from below. 



284. Region of Phototropic Curvature. Grow Bean 

 seedlings in darkness : when the epicotyl is 4 or 5 cm. long 

 mark it with ink lines at intervals of 5 mm., starting from 

 the apex. Expose to one-sided light, and note that the cur- 

 vature takes place in the actively growing upper region. 



285. Curvature and Turgidity. Cut off the plumules 

 of (A) a few Bean seedlings that have been exposed to 

 one-sided light only until the plumule has bent slightly, 

 (B) similar seedlings exposed for 24 hours. Put the two 

 lots in strong (15 or 20 per cent.) salt solution, in two 

 saucers. In A the curvature is diminished by plasmoly- 

 sis, because the difference in osmotic pressure between the 

 convex and concave sides has not yet been completely fixed 

 by growth ; in B the curvature is not affected by plasmo- 

 lysis, since it has now become fixed by growth. 



286. Transmission of Stimulus. Germinate seeds 

 of Wheat or Oats in darkness, in pots filled to the rim 

 with soil. When the shoots are about 2 cm. long expose 

 them to one-sided light. Examine them at frequent 



