54 FORMATION OF CHLOROPHYLL. [CH. II 



SECTION D. Conditions necessary for production 

 of chlorophyll. Etiolation. Sun- and shade-leaves, 



(65) Formation of chlorophyll 1 . 



Seedlings of mustard (Sinapis) are grown in the dark 2 

 and are then placed in the morning in a good light close 

 to the window, and the time necessary for the production 

 a of distinct green colour is noted ; some effect is visible 

 after one hour. 



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 

 chlorophyll, with control specimens left in the dark. They 

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

 In this way Elfving 3 showed that light increases the for- 

 mation of etiolin. 



(67) Pinus. 



Light is not necessary for chlorophyll formation in 



1 Wiesner, Die Entstehung d. Chlorophylls. Vienna, 1877. 



2 Etiolation proper can only be observed in parts of plants which 

 have developed in the dark. The already formed chlorophyll may 

 become discoloured by starvation, but this is not etiolation. Many 

 leaves retain their green colour for a long time in darkness. 



3 Sachs' Arbeiten, n. p. 495. 



