5 8 PLANT PHYSIOLOGY. 



Ordinary dry battery-cells, with any quick-acting circuit-closer, are 

 ample, and for convenience may be arranged as shown in Fig. 9. For an 

 induction-coil, any small form (borrowable usually from the Department 

 of Physics) will do. 



An inexpensive electrical slide maybe purchased in the Arthur Ap- 

 paratus (see page 32), or may be made by cementing small binding- 

 screws and strips of brass to an ordinary slide by sealing-wax, or yet more 

 simply as follows (see Fig. 9) : The clips belonging to the microscope- 

 stage are insulated by pushing them into place surrounded by thin silk 

 or rubber; their free ends are then brought within half of an inch of one 

 another over an ordinary slide; thin strips of tin-foil are placed beneath 

 them and the ends brought but a sixteenth of an inch apart ; the Nitella 

 cell is then placed with its ends on the tin-foil poles, is covered with water 

 and a "^over-glass, and the whole is ready for use. After the exact tem- 

 perature-measurements of Exercise 9 it does not seem profitable to take 

 time for very detailed quantitative measurements of effects of electricity, 

 though this may readily be done by aid of electrometers. 



12. What effect is produced upon Protoplasm, as manifested in 

 its rate of movement, by mechanical shock ? 



Answer from the results of simple experiments invented by 

 yourselves (call them Experiment 4). 



Remember the golden rule of experiment, --to alter but 

 a single condition. 



13. What effects are produced upon living Protoplasm by 

 chemical substances? 



This subject, though of much importance, cannot here be 

 taken up practically, and it is to be worked out from your 

 various sources of information and expressed concisely in a 

 paragraph. It is necessary to distinguish very clearly between 

 the direct chemical effects produced by the chemicals upon the 

 Protoplasm, and the irritable responses produced by chemicals 

 acting as stimuli. The former alone are to be discussed here, 

 while the latter will be studied later under Irritability. 



There is one phase of the subject not difficult of experiment, i.e., the 

 effects of anaesthetics, and of other gases, upon protoplasm as shown by 

 the cytoplasmic movement. Full directions for this are given by Detmer, 

 422, and by Darwin and Acton, 18. An excellent gas-slide for the pur- 

 pose is supplied in the Arthur apparatus. 



Experiments on chemotropism will be referred to under Irritability. 



