36 



PHYSIOLOGY. 



water on the surface, and place them under a glass bell jar, which 

 is tightly closed below but which contains no water. Now place 

 this in a brightly Hghted window, or in sunlight. In the course 

 of fifteen to thirty minutes we notice that a tliin film of moisture 

 is accumulating on the inner surface of the glass jar. After an 

 hour or more the moisture has accumulated so that it appears in 

 the form of small drops of condensed water. We should set up 

 at the same time a bell jar in exactly the same way but which 

 contains no leaves. In this jar there is no condensed moisture 

 on the inner surface. We thus are justified in concluding that 



Fig- 47- 

 After a few hours drops of water have accumulated on the inside of the jar covering 



the leaves. 



the moisture in the former jar comes from the leaves. Since 

 there is no visible water on the surfaces of the leaves, or at the 

 cut ends, before it may have condensed there, w^e infer that the 

 water escapes from the leaves in the form of vjater vapor, and 

 that this water vapor, when it comes in contact with the surface 

 of the cold glass, condenses and forms the moisture film, and 

 later the drops of water. The leaves of these cut shoots there- 

 fore lose water in the form of water vapor, and thus a loss of 

 turgidity results. 



70. Loss of water from growing plants. — Suppose we now 

 take a small and actively growing plant in a pot, and cover the 

 pot and the soil v/ith a sheet of rubber cloth or flexible oilcloth 



