242 MOVEMENT IN PLANTS. 



sticks or other supports used must not be very thick, since 

 the tendrils cannot coil around a thick support. 



But since Pea tendrils make somewhat slow responses 

 to stimuli, obtain if possible plants of Sicyos angulatus, 

 Cyclanthera explodens, or Echinocystis lobata all belong- 

 ing to the Cucurbitaceae and easily raised from seed ; other 

 members of the same family are White Bryony which 

 answers fairly well and (with much less sensitive tendrils) 

 Cucumber and Marrow. In. some species of Passion-flower 

 the tendrils are sensitive enough for most experiments ; 

 those of Vine are much less so. 



330. Growth of Tendril before Contact. In Sicyos, 

 for instance, note that the tendrils as they develop from 

 the bud are rolled up spirally, the convex side being the 

 morphologically lower side; in a few days the tendril 

 straightens out, performing meanwhile revolving move- 

 ments ; when these movements cease, the tendril elongates 

 rapidly, growth being greatest in the lower half of the 

 tendril and amounting to about 50 per cent, or even more 

 per day for three to five days ; then for a few days the 

 tendril grows slowly ; then one-sided growth begins, the 

 upper side growing more rapidly than the lower and thus 

 causing the formation of a spiral the concave side being 

 now the morphologically lower side of the tendril. Care- 

 fully observe all these points ; mark the tendrils with ink 

 lines into zones and note the rate of growth daily. 



331. Localisation of Responsiveness. E-ub a tendril 

 gently at different points with a thin stick, and note that 

 it is most irritable near the free end and on the lower side 

 (which is slightly concave in the young tendril ready to 

 attach itself) ; if the upper side is rubbed, even in this 

 terminal region, no curvature takes place. 



332. The Response to Stimulation. Rub the inside 

 of the terminal slightly hooked portion of a young tendril 

 with a pencil or stick ; the tendril soon shows a distinct 

 curve, and forms a complete ring in a time varying accord- 

 ing to the species and the external conditions about six 



