9 8 



GROWTH AND WORK OF PLANTS 



placed under a dry bell jar or inverted fruit jar, 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 moisture 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 accurhulates on the 

 inside of the glass vessel indicates that the leaves in their normal 

 position on the plant give off water. 



158. 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 de- 

 scribed 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. 

 85. The cobalt paper should 

 first be dried by heat so that 

 it is blue. In a very short time the cobalt paper 

 under the jar with the plant will begin to redden, 

 while the paper under the other jar is still blue. 

 The blue cobalt paper is very sensitive to moisture and a little 

 moisture in the air will quickly redden it before enough moisture 



* 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. 



Fig. 84. 

 Water vapor 

 is given off by 

 the leaves when 

 attached to the 

 living plant. It 

 condenses into 

 drops of water 

 on the cool 

 surface of the 

 glass covering 

 the plant. 



Fig. 85. 



A good way to show that 

 the water passes off from 

 the leaves in the form of 

 water vapor. 



