THE INFLUENCE OF CONTACT UPON TENDRILS 



57 



If two of the branches of the trifid tendril of this plant become attached 

 the other one usually persists also, but remains thinner and slightly shorter 

 than the attached ones. 



On the other hand the coiling of the long pulvinus of the terminal pair 

 of leaf-segments of Dalbergia lingo, around a support often leads to the 

 leaflets being thrown off, but this may also occur spontaneously without 

 apparent cause *. 



SECTION 13. The Influence of Contact upon the Growth and 



Curvature of Tendrils. 



Since we are dealing with growth-curvatures it is only natural that 

 a response should only be possible in organisms still capable of growth, 

 or in which the stimulus reawakens the power of growth. This applies not 

 only to the curvature of tendrils but also to the haustoria, sucking-disks, 

 and the coiling part of a petiole-climber in which the stimulus of contact 

 excites renewed growth or awakens a special form of productive activity. 



According to Fitting the growth of a curving tendril undergoes 

 a pronounced but temporary acceleration persisting during the reaction 2 . 

 This acceleration is especially great when the curvature is rapid, for the 

 median axis may elongate 20 to 100 times, and the convex side 40 to 200 



FIG. 18. Curves representing the growth of the convex and concave sides of the tendril of Pilogyne sttazn's 

 after stimulation at *. The curve for the median axis is taken as the mean between those for the concave and 

 convex sides. The horizontal distances give the times in minutes, the vertical distances (i division = 0-0121 mtn.^ 

 the growth as indicated by the divisions marked on the tendril previously to stimulation, and which had 

 remained the same distance apart during the previous 20 minutes. (After Fitting.) 



times as rapidly as before stimulation, and also after its effect has passed 

 away. After transitory stimulation the concave side, which either retains 

 the same length or only slightly shortens, begins to grow more actively, 

 and since the convex side has now ceased to elongate, the tendril soon 

 straightens. Similar results were obtained by Fitting with rapidly and 



1 Ewart, 1. c., p. 228. 



2 These studies, temporarily interrupted by the untimely death of Ockel, who began them at 

 Pfeffer's instigation, were completed by Fitting, Her. d. bot. Ges., 1902, p. 373; Jahrb. f. wiss. Bot., 

 1903, Bd. xxxvin, p. 545. 



