48 CHLOROSIS. [CH. II 



which is covered by a glass plate. A similar vessel 

 contains control plants and is allowed to remain at the 

 room temperature of about 15° C. 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. 



(69) Oxygen necessary for chlorophyll-formation. 



Germinate mustard in the dark and when the coty- 

 ledons are free from the seed coat pass 2 or 3 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 

 exposed to light, but they do not become green ; while 

 control plants placed on wet filter paper under a bell-jar 

 soon develope chlorophyll. It is not necessary to use 

 boiled water, the amount of air in ordinary spring water 

 being insufficient for the respiration of land-plants. 



(70) Seedlings in hydrogen. 



To demonstrate the fact in another way mustard seed- 

 lings may be placed in hydrogen. We use the L shaped 

 vessels recommended by Detmer'- The difference between 

 the experimental seedlings and the control in air is clear 

 after 24 hours. The vessel may be filled with hydrogen 

 by displacement of water.. 



(71) Iron. 



The effect of iron salts in restoring a green colour 

 to chlorotic^ leaves, may be occasionally demonstrated 

 on chance specimens. Professor Elfving of Helsiagfors, 



1 Praktikum, p. 26. ' See Sachs' Arbeiten, iii. p. 433. 



