TRANSPIRATION. 37 



which fits tightly around the stem of the plant so that the mois- 

 ture from the soil or from the surface of the pot cannot escape. 

 Then place a bell jar over the plant, and set in a brightly lighted 

 place, at a temperature suitable for growth. In the course of a 

 few minutes on a dry day a moisture film forms on the inner 

 surface of the glass, just as it did in the case of the glass jar con- 

 taining the cut shoots and leaves. Later the moisture has con- 

 densed so that it is in the form of drops. If we have the same 

 leaf surface here as we had with the cut shoots, we shall prob- 

 ably find that a larger amount of water accumulates on the 

 surface of the jar from the plant that is still attached to its 

 roots. 



71. Water escapes from the surfaces of living leaves in the 

 form of water vapor. This living plant then has lost water, which 

 also escapes in the form of water vapor. Since here there are no 

 cut places on the shoots or leaves, we infer that the loss of water 

 vapor takes place from the surfaces of the leaves and from the 

 shoots. It is also to be noted that, while this plant is losing 

 water from the surfaces of the leaves, it does not wilt or lose its 

 turgidity. The roots by their activity and pressure supply water 

 to take the place of that which is given off in the form of water 

 vapor. This loss of water in the form of water vapor by plants 

 is transpiration. 



72. A test for the escape of water vapor from plants. 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. 



73. Take two bell jars, as shown in fig. 49. Under one place 

 a potted plant, the pot and earth being covered by oiled paper. 

 Or cover the plant with a fruit jar. To a stake in the pot pin a 

 piece of the dried cobalt paper, and at the same time pin to a 



