CH. Il] ETIOLATION. 47 



Place similar etiolated plants in the darkest corner 

 of the laboratory and when chlorophyll has been developed 

 show, by an examination of the leaves with Sachs' test, 

 that light too weak for assimilation is strong enough for 

 chlorophyll-formation. 



(66) Etiolin and light. 



The following point is of less importance. Compare 

 the colour of etiolated seedlings, which have been exposed 

 to light for one or two hours but have not developed chlo- 

 rophyll, with control specimens left in the dark. They will 

 be found to be of a darker yellow or orange colour. In 

 this way Elfving^ showed that light increases the forma- 

 tion of etiolin. 



(67). Pinus. 



Light is not necessary for chlorophyll formation in 

 certain Gymnosperms. The seeds of various species of 

 Pinus should be sown 3 weeks or a month before they are 

 needed for demonstration. Let them be kept in the dark 

 continuously and at a temperature of at least 15° C. Peas, 

 or beans should be grown with them to prove by their 

 appearance that the cupboard is dark enough to etiolate 

 ordinary plants. 



(68) Temperature. 



Sink an empty beaker into a larger one half filled 

 with water, and keep the water at 30° or 31° C. by means 

 of a thermostat. Etiolated plants such as seedling cereals, 

 or the epicotyls of beans are placed in the inner beaker 



^ Saoh's Arbeiten, ii. p. 495. 



