KBUTJZKf 4J APPARATUS. 



273 



733. Vesque has devised an automatic apparatus 1 by which 

 the disturbance of the equilibrium of the balance as the water 

 evaporates can be recorded upon a revolving drum. In this 

 apparatus, as soon as the needle records the moment of descent 

 of the beam, an electrical current releases a valve so as to per- 

 mit the passage of a sufficient quantity of mercury to the losing 

 side of the balance to restore the equilibrium. 



734. The registering apparatus of Krutizky 2 is simple, but 

 unfortunately can be used only with 



cut stems or branches. It consists 

 of a U-tube filled with water, in one 

 end of which a leaf or stem (cut off 

 under water) is inserted, through a 

 tightly fitting cork. Through a cork 

 in the other end extends the short 

 leg of a siphon. In a jar of water 

 there floats a tube balanced to keep 

 it erect. This is somewhat like an 

 hydrometer (but open at the top), 

 and contains a certain amount of 

 water into which comes the long leg 

 of the siphon. When by evapora- 

 tion from the plant water is drawn 

 up through the siphon out of the 

 floating tube, the tube (called a 

 "swimmer") of course becomes 

 lighter and rises in the jar. If an 



index is attached to the swimmer, as in the figure, it can be used 

 to record upon a revolving drum the rise of the swimmer as the 

 plant transpires. To prevent evaporation from the water in the 

 jar and in the swimmer, its surface is covered by a film of oil. 8 



735. When a transpiring plant is placed under a bell-jar, a 

 certain amount of the transpired water will collect upon the 

 inside of the jar, often a sufficient quantity to appear as large 



1 For a full account of its construction see Annales des Sc. nat., ser. 6, 

 tome vi., 1878, p. 186. 



2 Botanische Zeitung, 1878, p. 161. 



3 A simpler piece of apparatus arranged by Pfeffer answers well for class 

 demonstration. It is easily understood from Fig. 147. The fall of water in 

 the small lateral tube is very marked, but attention should be called to the 

 varying pressure caused by the constantly changing level of the water in the 

 tube. 



FIG. 146. Krutizky's apparatus. 

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