128 



Elementary Plant Physiology. 



dril, and follow the movements of the tendril in coiling 

 around it. If the observation is continued over two or three 

 days, the formation of free coils in the free portion of the 

 organ may also be followed. Coat a glass rod with soft 

 gelatine, and touch the tendril. Does a reaction follow ? 

 Allow the gelatine to harden, and repeat test. Compare 

 results. Jar the tendrils of a vine by striking the stem. 

 Does a reaction follow ? Compare with results obtained by 

 similar tests with Mimosa (Figs. 99-102). 



140. Circumnutation of growing organs. — Plant 



\ 23 



Fig. 103. — Successive positions of stem of bindweed in twining around a support. 

 After Bonnier and Leclerc du Sablon. 



four seedlings of bean or morning-glory around the margin 

 of a large box or pot full of earth, and set a rod or support 

 upright in the center. As the stems elongate select a bright, 

 warm day, when the plant is growing rapidly, with the soil 

 well watered, and observe the successive positions occupied 

 by the tips of the stems. Support a sheet of glass over one 

 of the plants, and mark the positions of the apex of one of 

 the stems hourly during half a day. What length of time is 

 necessary for the stem to make a complete revolution and 

 return to a position corresponding most nearly to its original 

 position ? 



