160 LEAVES 



After ten or fifteen minutes note the result. 

 What occurs? Which paper changes color more quickly? 

 What may be inferred from this ? 



Note. Cobalt paper may also be used in the following manner: 

 If two bell jars are wiped dry and into each a piece of dried cobalt 

 paper is put, both will retain their blue color indefinitely because 

 the air remains dry. 



But if a plant or branch from a vigorous plant is placed in either 

 jar, the cobalt paper will soon begin to turn red, showing the pres- 

 ence of moisture in the air. This moisture can of course come only 

 from the plant, since the other paper retains its blue color. Other 

 modifications of this experiment will readily suggest themselves. 



Query. Do thin leaves give off water more quickly or less 

 quickly than thick ones? Does a cactus yield moisture as 

 easily as spinach or lettuce ? Compare rhododendron leaves 

 with rhubarb, and houseleek with geranium. 



143. LEAVES 



Object. To find how much water is given off by a 

 plant in a given time. 



Apparatus. A small, healthy potted plant having large leaves, 

 rubber cloth, and scales. 



Method. Weigh the plant after having watered it and 

 covered the flowerpot and soil up to the stem with the 

 rubber. The only exposed surface will thus be the stem and 

 other parts above ground: 



After three or four hours weigh the flowerpot again and 

 note the loss. If the plant has been carefully covered, the 

 loss must be due to water transpired through the leaves. 



Conclusion. Answers will vary with kind of plant, 

 number of leaves, and conditions of moisture in the atmos- 

 phere. 



