ETIOLATION OF SESSILE LEAVES 



II/ 



Note the development of both plants in 



temperature as above, 

 light and in darkness. 



177. Etiolation of Leaves with Parallel Veins. Secure a num- 

 ber of bulbs of Narcissus, or some similar plant, and force in dark 

 room or greenhouse in January or February. 



Compare the size, form and structure of the 

 normal and etiolated specimens. Compare also 

 the flowers in the two demonstrations. The 

 tender organs of the etiolated specimens should 

 be supported in order not to suffer damage by 

 bending from their own weight. 



178. Etiolation of Sessile Leaves. Force the 

 growth of some beets in 



dark room and compare 

 with normal individuals. 



179. Etiolation of 

 Climbing and Trailing 

 Plants. Grow a num- 

 ber of specimens of 

 Menispermum, Apios, 

 Falcata, or any of the 

 tuberous rooted Con- 

 volvulaceae in a dark 

 room. Compare the 

 position, form and structure 

 actions of the shoot to gravity, 

 persist ? 



180. Formation and Maintenance of Chlorophyl. Chloroplasts 

 are functionally active only when exposed to light, and generally 

 do not construct chlorophyl until stimulated to do so by light, al- 

 though many forms are capable of building and maintaining this 

 substance in total darkness. It is evident, therefore, that no 

 absolute minimum of intensity for this process is to be found, and' 

 no statement may be made as to the optimal stimulating effect. 

 The increase in the intensity of light may reach a point where 



as 



Viola rostrata (normal). 

 Viola rostrata (etiolated). 



above. Note also the re- 

 Do the nutating movements 



