WORK OF THE LEAVES: TRANSPIRATION 



and a similar vessel with no leaves under it is kept as a check. 

 In the course of an hour or so there will be seen a film of mois- 

 ture on the inside of the glass covering the leaves, while the 

 other glass will remain dry. The moisture came from the leaves 

 through the surface. To show this with an entire plant, the pot 

 and soil of a plant with a goodly number of leaves are covered 

 with rubber cloth to prevent the escape of moisture from the soil 

 or pot. The plant is now covered with a glass bell or fruit jar so 

 that moisture cannot escape below. The moisture which accu- 

 mulates on the inside of the glass vessel indicates that the leaves 

 in their normal position on the plant give off water. 



154. Form in which the water escapes from the plant. 

 This can be shown by a very interesting experiment. A plant is 

 covered with a bell jar as described above, and at the same time 

 a piece of cobalt paper * pinned to a stake is placed under the 

 glass vessel. At the same time 

 another piece of cobalt paper 

 is placed under a similar dry 

 glass jar with no plant under 

 as shown in fig. 82. The co- 

 balt paper should first be dried 

 by heat so that it is blue. In 

 a very short time the cobalt F te- 8l - Fi g- 82 - 



j ,1 .,1 ,1 Water vapor A good way to show that 



paper Under the jar With the is given off by the water passes off from the 



i .11 i 11 1.1 the leaves when leaves in the form of water 



plant will begin to redden, while attached to the vapor. 

 the paper under the other jar conden P ses nt into 



paper is very sensi- 

 moisture in the air 

 enough moisture has 

 This demonstrates 



is still blue. The blue cobalt onthe SJ 



tive to moisture and a little coverfng he gl the 



will quickly redden it before plal 



been given off to show on the glass jar. 



that the water escapes from the leaves in the form of water 



* Make a solution of cobalt chloride in water. Saturate several pieces 

 of filter paper with it. Allow them to dry. The water solution of cobalt 

 chloride is red. The paper is also red when it is moist, but when it is 

 thoroughly dry it is blue. It is very sensitive to moisture and the moisture 

 of the air is often sufficient to redden it. Before using, dry the paper in an 

 oven or over a flame. 



