CH. IT] FORMATION OF CHLOKOPHYLL. 55 



certain Gymnosperms 1 . The seeds of various species of 

 Piiius should be sown three 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 2 . 



Sink an empty beaker in 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 seedlings of Sinapis 

 or the epicotyls of beans are placed in the inner beaker, 

 which is covered by a glass plate. A similar vessel 

 contains control plants and is allowed to remain at a 

 room temperature of about 15G. After 2 or 3 hours a 

 distinct difference in the greenness of the plants at 31 C. 

 as compared with the control plants is perceptible. In 

 one experiment with mustard seedlings, in which the 

 control plants were kept at a temperature of 10 C., a 

 distinct effect was perceptible in one hour. 



(69) Oxygen necessary for chlorophyll-formation. 



Germinate mustard in the dark and when the coty- 

 ledons are free from the seed-coat pass two or three plants 

 under the rim of an inverted test-tube filled with water. 

 They float 3 up to the top of the tube and are thus fully 



1 Sachs' Physiologic (French Trans.), p. 8. 



2 Sachs, loc. cit. p. 11. 



3 If the seedlings sink instead of floating, as sometimes happens, they 

 may be allowed to lie at the bottom of a beaker of water. 



