1 8 RELATIONS OF PLANTS TO MECHANICAL FORCES 



25. Summation of Impulses. Secure a few good specimens 

 of Dionaea growing in pots at a temperature of 25 to 30 C 

 Observe the mechanism of the curiously formed leaves. Objects 

 roughly placed on the upper surfaces of the lobes cause them to 

 fold up together applying the inner (upper) sides together. Now 

 carefully touch one of the strong hair-like bodies growing up from 

 each lobe of a plant hitherto undisturbed. If a firm gentle blow 

 be given with a thin splinter of wood in such manner that but one 



FIG. 5. Dionaea liiuscipula. I, open normal leaf. 2, closed. 3, irritable- 

 spines (X 5)- 4> glands on surface of leaf (X 100). After Green. 



shock is given to the hair no movement will follow. Repeat the 

 blow on the same hair or any hair of the leaf within ten or fifteen 

 seconds and the characteristic closure of the lamina will result. 

 Give the blows with an interval of thirty seconds between and 

 note result. Give a succession of very light blows separated by 

 twenty- five to forty seconds. How many are necessary to secure 

 movement P 1 



1 Dean, B. Dionaea. Its life habits and conditions. Trans. N. Y. Acad Sci. 

 12: 9. 1892. See also, MacFarlane, J. M. Contributions to the history of Dionaea 

 muscipula, Ellis. Cont. Bot. Lab. Univ. Penn. i : 7. 1892. 



