66 PLANT PHYSIOLOGY 



diate, the result is proportional to its intensity, no question of 

 advantage or disadvantage to the organism is involved, and 

 the Protoplasm is purely passive and responseless. The study 

 of such direct relations belongs rather to physics and to chemis- 

 try than to physiology, and, in their simpler manifestations, 

 they are usually somewhat obvious. Yet, if the student have 

 time and the will to observe some of them for himself, he may 

 do so through the following: 



Suggested Experiments. For these the living Protoplasm is selected 

 as before and mounted for the microscope. 



Heat. Place the slide on a metal plate perforated under the objective 

 and clamped, with an intervening thick felt or cloth, to the microscope stage; 

 apply heat to a projecting part with a spirit-lamp, and observe the Protoplasm 

 through the various changes to disintegration. 



Mechanical Effects. Apply pressure with needles upon the cover-glass, 

 and observe the disorganization effects up to complete destruction. 



Chemical Action. Apply upon one side of the cover-glass a drop of 10% 

 solution of caustic potash ; draw it under by filter-paper applied at the oppo- 

 site margin; continue from time to time, and observe the result upon the 

 Protoplasm. 



Gravitation. Select material, such as Tradescantia, which has a conspicu- 

 ous nucleus, and mount it so that when the microscope is set horizontally 

 the nuclei will be at the upper ends of the cells; from time to time note the 

 result upon their positions. 



Or mount a streaming cell of Nitella after the manner described by 

 Ewart, 23-25, so that it will be vertical when the microscope is horizontal; 

 observe, by aid of measurement, whether the more solid particles move at 

 the same rate up and down. • 



Electricity. Arrange, by the method described on page 71, a stream- 

 ing cell, so that its ends are in contact with tin-foil strips which can be thrown 

 into circuit with 1, 2, 3, or 4 dry battery cells, and note effects upon the Proto- 

 plasm. Test also, if practicable, the effects of an equivalent induced current. 



Light. Prepare a slide of some material which develops naturally in 

 darkness or in dim light, e.g., a root-hair, and, taking precautions to prevent 

 action of heat (Part III), focus upon it the fullest possible obtainable light, 

 and note result. Here consider the germicidal power of light and its sup- 

 posed physico-chemical basis. 



The second of the three ways in which external forces may 

 act upon Protoplasm happens to be illustrated with great clear- 

 ness by the action of heat upon protoplasmic* streaming, a mat- 

 ter which should now receive careful experimental study. 



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