ICE, WATER, AND STEAM 



115 



of water there. A great deal of water evaporates from the 

 surface of the land also, but of course not so much as frOm 

 a free water surface. 



128. Evaporation from plants : transpiration. The evapora- 

 tion of water from land is greatly accelerated by plants. Trees, 

 grasses, weeds, cultivated crops in fact, all common land 

 plants absorb water from the soil, and most of this water 

 may afterwards evaporate 

 from the leaves. 



Usually we are not aware 

 that water is evaporating 

 from the leaves of plants, 

 since it passes off as a gas 

 and is therefore not visible. 

 There are ways in which 

 it can be made visible. A 

 demonstration of this may 

 be made by inclosing sev- 

 eral leaves in a bottle or 

 tumbler (fig. 62) in such a 

 way that there is little 

 chance for water to enter 

 or leave the bottle except- 

 ing through the leaves. 

 The water given off from 

 the leaves soon saturates the 

 space in the bottle, and 

 the excess is deposited on the inside of the bottle. Anyone 

 can easily perform the experiment for himself. If the leaves 

 are removed from the plant, they should be placed with their 

 lower ends in water. 



A more satisfactory way to show the loss of water is to 

 weigh a potted plant from time to time, having first wrapped 

 the pot in sheet rubber (why?). If the area of the leaves 

 is ascertained, it is possible to know just how much water 



FIG. 62. Transpiration by leaves 



Some of the water which evaporates 



from the leaves condenses upon the inside 



of the bottle 



