38 



PHYSIOLOGY. 



stake, in another jar covering no plant, another piece of cobalt 

 paper. They should both be p>ut under the jars at the same 

 time. In a few moments the paper in the jar with the plant will 

 begin to redden. In a short while, ten or fifteen minutes, prob- 

 ably, it will be entirely red, while the paper under the other jar 

 will remain blue, or be only slightly reddened. The water vapor 

 passing off from the living plant comes in contact with the sensi- 



Fig. 48. Fig. 49. 



Fig. 48. — Water vapor is given off bv the leaves when attached to the H\'ing plant- 

 It condenses into drops of water on the coi >1 surface of the glass covering the plant 



Fig. 49. — A good way to show that the water passes ofi from the leaves in the form 

 of water vapor. 



five cobalt chloride in the paper and reddens it before there is 

 sufficient vapor present to condense as a film of moisture on the 

 surface of the jar. 



74. Experiment to compare loss of water in a dry and a 

 humid atmosphere. — We should now coinpare the escape of 

 water from the leaves of a plant covered bv a bell jar, as in the 

 last experiment, with that which tal^cs place when the plant is 



