108 TENDRIL-CLIMBERS [CH. 



has been sought to show that twining plants are all more 

 or less irritable ; however this may be, it is at least clear 

 that the irritability of ordinary twining shoots is of a far 

 lower order than in the case of the true tendrils to which 

 we now turn. 



The highest adaptations for climbing are met with in 

 tendril-climbers, not only because they develope special 

 organs, the tendrils, for grasping supports, but also on 

 account of the extraordinarily beautiful irritable pheno- 

 mena displayed by these organs. 



The simplest form of tendril climbing is shown by 

 plants like the Garden Nasturtiums {Tropceolum) where 

 the long petiole of an ordinary leaf coils itself once or 

 twice round a stick or twig, and so obtains a hold-fast. 

 Similarly with Maurandia, Solanum, Convolvulus and 

 Antirrhinum cit^hosum. In Fumaria, Clematis and Atra- 

 gene the same coiling propensity is observed in the 

 petiolules of the leaflets ; while in other cases — Nepenthes, 

 Gloriosa, Flagellaria, Mutisia, and some Fritillarias — it is 

 the rachis or prolonged midrib which coils. 



In the remarkable case of the climbing Ferns Lygo- 

 dium, the twining is effected by the entire rachis, which 

 goes on growing for several seasons, and it is difficult to 

 decide whether this should be regarded as a tendril- 

 climber or as a twining-plant. 



As we advance through the numerous forms known 

 the tendril is found to become more and more a special 

 organ, which in its most highly developed condition is 

 thin, long and filamentous in shape, and so distinctly 

 iri'itable that even a few strokes with a pencil, or at most 

 a few minutes contact with a stick, suffice to so irritate 

 the touched side that it grows more slowly than the side 

 not touched. The consequence is that the tendril coils 

 round the stick or other solid object. 



