54 PLANT PHYSIOLOGY. 



7. What is the exact rate of movement in these two plants 

 under ordinary conditions? 



Answer by precise quantitative measurements. 



To make these it is necessary to observe how long it takes for some 

 of the swiftest-moving granules in the Protoplasm to pass over a given 

 space. Time may be measured by a metronome (see Fig. 8) ticking 

 seconds, and space by an ocular micrometer, the relative value of 

 the scale of the latter being first determined by use of a stage mi- 

 crometer. The temperature of the room should be noted. 



(Cells showing tlie most active movement should be selected. To allow 

 of comparison of results between students, measurements should all be 

 expressed in the same units, preferably mm., per minute taken for the 

 even degrees. Use fiat mirror to avoid focusing of heat ; do not 

 pitic/i the cell with forceps ; do not iise material recently chilled by 

 cold air.) 



8. What are the various classes of external influences which 

 can be brought to bear upon living Protoplasm? 



Answer by a classified table worked out by yourselves. 



Of the various external influences which can readily be 

 brought to bear upon Protoplasm, the most important are: 



(1) Temperature changes. 



(2) Light. 



(3) Electricity. 



(4) Mechanical Shock. 



(^5) Chemical Substances.* 



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

 its rate of movement, by changes of temperature ? 



Answer by Experiment I. 



EXPERIMENT i. To determine this, some method is needful by 

 which the temperature of a given protoplast may be raised and 

 lowered at will, while the rate of cytoplasmic movement is determined 

 at each degree. Measurements may be made as already done under 

 Exercise 7 ; temperature may be controlled by the temperature-stage 



* Gravitation and some others are here omitted, because this section is not con-, 

 cerned with active responses to external influences acting as stimuli (which are later 

 to be studied under Irritability), but with the direct (mechanical, physical, and chem- 

 ical) effects produced by outside influences upon protoplasm. The distinction is 

 important, though of course the two merge into one another, and are often indistin- 

 guishable. 



