Cuap. V. CONCLUDING REMARKS. 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- 
