CH. Il] FORMATION OF CHLOROPHYLL. 55 



certain Gymnosperms\ The seeds of various species of 

 Finns 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^. 



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 jolants such as seedlings of Sinajns 

 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 15*^0. 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 ^ up to the top of the tube and are thus fully 



1 Sachs' Physiologie (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. 



