Chap. 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 Echinocijstis 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 Echinocijstis 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 davs after 

 all revolving movement has ceased. A full-grown 

 tendril of Passiflora quadrangular is 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 



