12 RELATIONS OF PLANTS TO MECHANICAL FORCES 



Fig. 2. Successive positions 

 of Mimosa after stimulus has been 

 applied to tip of leaf. A, position 

 a few seconds after stimulus has 

 been applied at f. £, after im- 

 pulse has reached the base of the 

 leaf. C, after the effect of the 

 stimulus has been transmitted to 

 the entire body of the specimen 

 and is traversing one leaf from 

 base to apex. 



pare reactions in different species. 

 Crush a few cells and note appearance 

 of protoplasm. 



The shock given the material in 

 mounting it on the slide, and the con- 

 tact with water may stop the move- 

 ment, so that it is often necessary to 

 wait a few minutes for its resumption. 

 It is important to keep in mind the fact 

 that the cells of the organs affected in 

 the following experiments undergo 

 similar changes in response to shock, 

 although all living cells do not show 

 such distinct moving strands. 



18. Motile Reactions of a Higher 

 Plant to Mechanical Shock. Provide 

 a well-grown specimen of Mimosa 

 pudica, or any of the nearly related 

 and similarly irritable species, and place 

 it in the greenhouse or experimental 

 chamber where it will be kept at a 

 temperature of 25 to 30 ° C. in a moist 

 atmosphere, and the soil well supplied 

 with water. After a period of com- 

 plete rest of a day, in which the spec- 

 imen has not been jarred or jostled, 

 strike a quick sharp blow on the tip of 

 one of the expanded pinnules with a 

 pencil, or give it a snip with a pair of 

 forceps. Note the immediate change 

 in position of the parts actually struck, 

 the successive closure of the pairs of 

 pinnules toward the base of the leaflet, 

 the following slight movement of the 

 leaflets, and the change in the angle 



