Growth Movements 501 



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left flank may be differentiated. They usually complete 

 their growth within a few days, so that the plant may be 

 attached to its supports almost as rapidly as the shoot 

 elongates. 



The terminal part of the tendril is the more perceptive 

 region, and commonly the under surface exhibits greater 

 sensitiveness. Both surfaces and flanks may, however, 

 respond to contact stimuli. When the tendril is from 

 one-fourth to one-third grown, it exhibits marked auto- 

 nomic nutations, and the swinging of the tip through space 

 brings it into contact with any objects in the range of this 

 motion or of swaying movements caused by wind. Scrap- 

 ing the surface of the tendril against a suitable support 

 (especially repeated scraping) is followed by coiling and 

 close attachment around the object. The tendril is now 

 fixed at both ends, the prompt grasping of the support 

 being in part, apparently, due to turgor movements. 

 After attachment growth proceeds more rapidly on the 

 upper surface, and the tensions resulting throw the tendril 

 into a close coil, once or more reversed. 



Fixation by means of tendrils affords not merely secure 

 support, but the attachment at many points affords a 

 general elasticity and freedom from severe shock well 

 known through the principle of vehicle and car springs. 



304. Chemotropism. - The curvature and growth of 

 roots, pollen-tubes, or fungous hyphae in response to the 

 stimulus of chemical agents is chemotropism. At one 

 time it seemed that chemotropic response, especially 

 positive chemotropism, might commonly determine the 

 direction of growth in roots, penetration of parasitic fungi, 

 and other phenomena. Further study has developed the 



