72 



Elementary Plant Physiology. 



Any loss of weight from this preparation should be due to the 

 transpiration of water from the leaves. Set the plant on one 

 pan of the balance, together with a small measuring-glass, and 

 add weights to the other pan to bring the balance to an equi- 

 librium. Four hours later note the condition of the balance. 

 Fill a burette with water to the level of one of its divisions. 

 Carefully run water from the burette into the measuring-glass 



on the pan until the 

 balance is brought back 

 to its original position. 

 The amount of water in 

 the glass will represent 

 the transpiration. Note 

 the temperature of 

 the air around the 

 plant during the experi- 

 ment. Take the cloth 

 from the plant, and 

 ^\■ater it in the usual 

 manner. On the follow- 

 a lower or higher tem- 

 Compare results. 



Fig. 51. — Balance for estimation of amount of 

 transpiration. After Oels. 



ing day repeat the test as before, at 

 perature, ^\-ith the plant prepared as before 

 Make other tests in sunlight and shade. 



66. Guttation. — Procure a number of seedlings of wheat 

 (Triticiiui), corn {Zea), rice {Oryzd), or young plants of 

 Coleus, growing in soil in a pot, and set on a glass plate. \\'ater 

 freely, and then cover with the bell jar. A few hours later note 

 the exudation of drops of water at various points on the plant. 

 Make a careful sketch of two or three specimens, showing exact 

 location of drops. Remove the bell jar and note results. Make 

 a careful examination of sections through the parts on which 

 drops of water had collected, in a search for water pores and 

 outlets for liquid under pressure. The exudation pressure of 

 the living cells forces water into the vessels and other dead 



