208 



A YEAR IN SCIENCE 



carried 011 only by living material, for man has never 

 succeeded in producing living from non-living material. 

 Transpiration. Water plays an important part in 

 the life of plants. It is the most important single 

 factor which determines the way plants grow and 

 where they grow. All plant activity depends upon its 

 presence in considerable amount. Although there is 

 great and continual need of water, and although fre- 

 quently the supply is inadequate, still there is always 

 an enormous loss by way of the surface of the leaves. 

 This evaporation, or passing of the water from the leaves, 



is known as transpiration. 

 Since this water passes off in 

 the form of a gas, we are 

 usually not aware that water 

 is constantly evaporating 

 from the leaves of plants. 

 There are several ways, how- 

 ever, by which this can be 

 demonstrated. When a potted 

 plant, the pot of which has 

 been carefully wrapped in 

 sheet rubber to prevent the 

 Fig. si. Experiment to escape of moisture, is placed 



show transpiration. The . 



water which evaporates under a belljar, Within a 

 from the leaves condenses on 



few hours drops of water 



collect on the inside of the belljar. The amount of 

 water lost by a plant can be determined by weighing a 

 potted plant, so covered that no moisture can escape 



