SPONTANEOUS MOVEMENTS IN PLANTS. 



:S 7 



with some exceedingly sensitive plants, the falling of drops of rain on 

 the tendril will produce no effect whatever. The mode in which a 

 tendril of a Bignonia catches hold of a support is thus described by- 

 Darwin : " The main petiole is sensitive to contact with any object ; 

 even a small loop of thread after two days caused one to bend up- 

 ward. The whole tendrils are likewise sensitive to contact. Hence, 

 when a shoot grows through branched twigs, its revolving movement 

 soon brings the tendril into contact with some twig, and then all three 



Fig. 4. 



' toes ' bend (or sometimes one alone), and, after several hours, seize 

 fast hold of the twig, exactly like a bird when perched." The Virgin- 

 ian creeper has another mode of attaching itself to a wall or other solid 

 support, by the formation, at the extremities of the branches of the ten- 

 dril, of little disks or cushions, very similar to the disks on the foot of 

 the house-fly, by which it is enabled to attach itself to our windows, 

 and to walk along the ceiling. These disks secrete a glutinous fluid, 

 which attaches the tendril to the support with such strength that it is 

 often impossible to detach it without destroying the tendril, or even 

 removing a portion of the wall itself. As soon as the attachment is 

 accomplished, the tendril gradually thickens, and contracts spirally, as 

 shown in Figs. 3 and 4. This spiral contraction, indeed, is always the 

 result of the tendril meeting with a support ; and, if no support is 

 found, the tendril soon shrinks and withers away. Some tendrils ex- 

 hibit a most remarkable power of selection, which, to use Mr. Darwin's 

 words, " -would, in an animal, be called instinct." The tendrils of a 

 species of Bignonia slowly travelled over the surface of a piece of 

 wood, and, when the apex of one of them came to a hole or fissure, it 

 inserted itself; the same tendril would frequently withdraw from one 



