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THE POPULAR SCIENCE MONTHLY 



to obey, and therefore remained motionless. It was in reality ex- 

 tremely sensitive to a touch on any one of its sides. 



There is a remarkable movement which occurs in tendrils after they 

 have caught an object, and which renders a tendril a better climbing 

 organ than any sensitive leaf. This movement is called the " spiral con- 

 traction," and is shown in Fig. 4, which represents the spirally contracted 

 tendril of the wild bryony ; it may also be seen in Fig. 5, which repre- 

 sents the tendrils of the Virginia creeper. When a tendril first seizes 



Fig. 5. Ampelopsis hederaria. A. Tendril fully developed, with a young leaf on the opposite 

 Bide of the stem. B. Older tendril, several weeks after its attachment to a wall, with the 

 branches thickened and spirally contracted, and with the extremities developed into disks. 

 The unattached branches of this tendril have withered and dropped off. 



an object it is quite straight, with the exception of the extreme tip, 

 which is firmly curled round the object seized. But in a day or two 

 the tendril begins to contract, and ultimately assumes the corkscrew- 

 like form represented in the figures. It is clear that in spirally con- 

 tracting the tendril has become considerably shorter ; and, since the 

 end of the tendril is fixed to a branch, it is obvious that the stem of 

 the bryony must be dragged nearer to the object which its tendril has 

 caught. Thus, if a shoot of bryony seizes a support above it, the con- 

 traction of the tendril will pull up the shoot in the right direction. So 



