Cuar. IV. SPIRAL CONTRACTION, 159 
object. There is no such movement in any leaf- 
climber, with the exception of an occasional trace of 
it in the petioles of Tropzolum tricolorum. On the 
other hand, the tendrils of all tendril-bearing plants, 
contract spirally after they have caught an object with 
the following exceptions. Firstly, Corydalis claviculata, 
but then this plant might be called a leaf-climber. 
Secondly and thirdly, Bignonia unguis with its close 
allies, and Cardiospermum; but their tendrils are so 
short that their contraction could hardly occur, and 
would be quite superfluous. Fourthly, Smilax aspera 
offers a more marked exception, as its tendrils are 
moderately long. The tendrils of Dicentra, whilst the 
plant is young, are short and after attachment only 
become slightly flexuous; in older plants they are 
longer and then they contract spirally. I have seen 
no other exceptions, to the rule that tendrils, after 
clasping with their extremities a support, undergo 
spiral contraction. When, however, the tendril of a 
plant of which the stem is immovably fixed, catches 
some fixed object, it does not contract, simply because 
it cannot; this, however, rarely occurs. In the 
common Pea the lateral branches alone contract, and 
not the central stem; and with most plants, such as 
the Vine, Passiflora, Bryony, the basal portion never 
forms a spire. 
T have said that in Corydalis claviculata the end of 
the leaf or tendril (for this part may be indifferently 
so called) does not contract into a spire. The 
branchlets, however, after they have wound round 
