Cuar. IV. SPIRAL CONTRACTION. 161. 
tendril then forms a more or less open spire. A 
similar result follows if the extremity has caught 
some object, and is thus held fast. « 
The tendrils of many kinds of plants, if they catch 
nothing, contract after an interval of several days or 
weeks into a spire; but in these cases the movement 
takes place after the tendril has lost its revolving 
power and hangs down; it has also then partly or 
wholly lost its sensibility; so that this movement can 
be of no use. The spiral contraction of unattached 
tendrils is a much slower process than that of attached 
ones. Young tendrils which have caught a support 
and are spirally contracted, may constantly be seen on 
the same stem with the much older unattached and 
uncontracted tendrils. In the Echinocystis I have seen a 
tendril with the two lateral branches encircling twigs 
and contracted into beautiful spires, whilst the main 
branch which had caught nothing remained for many 
days straight. In this plant I once observed a main 
branch after it had caught a stick become spirally 
flexuous in 7 hrs., and spirally contracted in 18 hrs. 
Generally the tendrils of the Echinocystis begin to 
contract in from 12 hrs. to 24 hrs. after catching 
some object; whilst unattached tendrils do not begin 
to contract until two or three or even more days after 
all revolving movement has ceased. A full-grown 
tendril of Passiflora quadrangularis which had caught 
a stick began in 8 hrs. to contract, and in 24 hrs. 
formed several spires; a younger tendril, only two- 
thirds grown, showed the first trace of contraction in 
8 
