Chap. V. CONCLUDING KEMAEKS. 197 



in certain branches alone being thus modified, whilst 

 others remained unaltered; for we have seen with cer- 

 tain varieties of Phaseolus, that some of the branches 

 are thin, flexible, and twine, whilst other branches 

 on the same plant are stiff and have no such power. 



If we inquire how a petiole, a branch or flower- 

 peduncle first became sensitive to a touch, and 

 acquired the power of bending towards the touched 

 side, we get no certain answer. Nevertheless an ob- 

 servation by Hofmeister* well deserves attention, 

 namely, that the shoots and leaves of all plants, whilst 

 young, move after being shaken. Kerner also finds, as 

 we have seen, that the flower-peduncles of a large 

 number of plants, if shaken or gently rubbed bend to 

 this side. And it is young petioles and tendrils, 

 whatever their homological nature may be, which 

 move on being touched. It thus appears that climbing 

 plants have utilized and perfected a widely distributed 

 and incipient capacity, which capacity, as far as we 

 can see, is of no service to ordinary plants. If we 

 further inquire how the stems, petioles, tendrils, and 

 flower-peduncles of climbing plants first acquired 

 their power of spontaneously revolving, or, to speak 

 more accurately, of successively bending to all points 

 of the compass, we are again silenced, or at most can 

 only remark that the power of moving, both spon- 

 taneously and from various stimulants, is far more 



* Quoted by Cohn, in his handl. der Schlesischen Gesell. 

 remarkable memoir, " Contractile 1861, Heft i. s. 35. 

 Gewebe im Pflanzenreiche," ' Ab- 



