PHYSIOLOGICAL PROCESSES IN PLANTS 101 



with vaseline. Also be sure to vaseline the petioles at the 

 tips. Why ? Exactly balance the leaves on the pans and put 

 the scales in a sunny place. 



Conclusions. 1. Through which surface of a leaf does 

 transpiration take place ? 



2. How do you arrive at your conclusions ? 



FIG. 30. Experiment to show through which surface of a leaf transpiration 



takes place. 



Method b. {Optional.} 1. Insert a vigorous leafy branch in a cork 

 borer to fit, that has previously been forced through a rubber stopper. 

 .Withdraw the borer, leaving the branch firmly fixed in the stopper. 

 Press the stopper into the neck of a bottle of water. Set the bottle on a 

 glass plate and cover it with a bell jar with vaselined rim so that it fits 

 snugly. Place the apparatus in sunlight. Does moisture collect on the 

 inner surface of the bell jar ? 



Note. The experiment may be extended by weighing the stoppered 

 bottle of water to see if there is any loss of weight. Is the loss of weight 

 more rapid in sunlight or otherwise ? 



Conclusions. 1 . What condition favors rate of transpiration, or get- 

 ting rid of excess water from leaves ? 



2. What happens when a plant wilts ? 



3. Why are plants kept fresh by placing them in water ? 



