EFFECT OF SHOCK UPON TRANSPIRATION 21 



reactions. Strike an expanded leaf and note the result. Shield 

 a small flame or heated wire and touch the tip of a leaflet and 

 observe the reaction. Snip the tip of another leaf with a pair of 

 forceps or cut away a portion with a pair of scissors. The re- 

 action is again shown. 



Place the second specimen where it will receive a strong stim- 

 ulating current of air and carry through a series of tests similar 

 to the above. A device consisting of a centrifuge with a small 

 pliant rod such as a strip of bamboo attached to one arm may 

 also be set up by which the stem may be given delicate and re- 

 peated blows, and the behavior of the plant followed through a 

 parallel course of reactions. 



28. Influence of Shock upon Metabolic and other Processes. 

 The effect of any stimulus is to set up new or additional molecular 

 movement in the protoplasm. These movements may result in 

 external movement as in previous experiments, entailing the re- 

 lease of energy and the increase of the metabolic processes con- 

 cerned. Still further the influence of the stimulus may increase 

 the respiration and other processes in addition to the specific 

 energy release. Shock is followed by the appreciable increase of 

 the excretion of carbon dioxide, the decrease of surplus foods in 

 the cell, and by an increase in the amount of water thrown off in 

 the transpiratory processes. The last named result is probably 

 due to the greater amount of water present or thrown into the in- 

 tercellular spaces by the contractile action of the cells. 



29. Effect of Shock upon Transpiration. Select a vigorously 

 growing specimen of a tomato, geranium, or some leafy twig, and 

 fasten it to a potometer (See transpiration and potometer). An 

 hour or two later after the rate of transpiration is fairly steady note 

 the rate at which water is taken up by the shoot. Arrange a 

 centrifuge in such position that a very thin strip of bamboo at- 

 tached to one arm will strike the stem as the apparatus revolves. 

 Run the centrifuge to give the stem a series of shocks for a period 

 of fifteen minutes, that will not injure the plant mechanically. 

 Now take readings on the potometer for the next fifteen minutes. 



