Chap. IV. SPIKAL 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 Tropseolum tricolor um. 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 Yine, Passiflora, Bryony, the basal portion never 

 forms a spire. 



I 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 



