16 RELATIONS OF PLANTS TO MECHANICAL FORCES 



23. Method of Transmission of Impulses in Mimosa and Similar 

 Plants. A system of long tube-like cells lying near the fibro- 

 vascular bundles, and generally turgid are supposed to be the 

 organs of conduction of impulses consisting of hydrostatic disturb- 

 ances of the contained fluid. The exact demonstration of such 

 transmission has not been made however. The extremely small 

 size of the vessels, would render the gross movement of the water 

 very difficult and slow on account of the enormous friction to be 

 overcome. Artificial impulses given the smooth ends of several 

 branches supporting normally expanded leaves by powerful pumps 

 and endosmotic solutions failed to secure a reaction. 1 Further- 

 more impulses may be transmitted through a section of dead 

 stem or petiole and cause a reaction as demonstrated by the author 

 and others. 2 This is of sufficient interest to warrant its repeti- 

 tion. Select a small vigorous specimen of Mimosa and place it in 

 a horizontal position. Wrap a section of the stem 2 cm. long 

 with two or three thicknesses of cloth. Pour a steady stream of 

 boiling water on this for five minutes. Repeat a second and third 

 time at intervals of half an hour. Drive a small stake in the earth 

 in the pot and secure the stem to it by means of suitable cords, 

 and set in an upright position. Care must be exercised that no 

 portion of the stem is injured beside the section touched by the 

 boiling water and wrapped with cloth. Suspend a small vessel 

 of water conveniently near, and run a strip of cloth from it 

 to the bandage around the stem to prevent the treated section 

 from drying out, and reducing its capacity for conduction of water 

 to the leaves. After all of the leaves have regained the normal 

 position and the plant has the proper temperature, give a harsh 

 stimulus to the stem by cutting into the cortex with a razor or if 

 leaves are to be found both above and below the killed section, 

 hold a burning match to the tips of a leaflet. The stimulus-effect. 



1 MacDougal. Mechanism of movement and transmission of impulses in Mimosa 

 and other sensitive plants. Bot. Gazette, 22: 293. 1896. 



*Nemec, B. Reizleitung und die Reizleitenden Strukturen bei den Pflanzen. 

 Jena. 1 90 1. 



