SEcr. II 



PHYSIOLOGY 



319 



afTorded by Tropaeolum, Maurandia, Solanum jasminoides, Nepenthes, etc. The 

 subsequent modifications occurring in more perfectly developed tendrils are not 

 noticeable in the case of petiolar tendrils, although the coiling portion of the leaf- 

 stalk of Solanum jasminoides does become strongly thickened and lignified ; 

 while the leaf-blades o^ Clematis, by remaining small for a time, enhance the 

 tendril-like character of their leaf-stalks, and by bending backwards also assist in 

 maintaining the initial contact with a support. At other times the midribs of 

 the leaf-blades themselves become prolonged, and assume the function of tendrils 

 [Gloriosa, Littonia, FlageUaria). In many species of Fximaria and Corijdalis, in 



addition to the leaf-stalks, even the stalks of the 

 leaflets twine around slender supports, while the 

 parasitic shoots of CusciUa (Fig. 196) are adapted 

 for both twining and climbing. In many tropical 

 plants axillary slioots are transformed into tendril- 

 like climbing hooks. Climbing parts of the thallus 

 occur in some Thallophyta (Florideae) C"'). 



II. 



Fig. 236. — Portion of a climb- 

 ing shoot of Awprlops'is 

 Veitchii. Tlie tendrils (R) 

 have fastened themselves to 

 a smooth wall by means of 

 holdfasts. 



Fio. 237. — Lopliospermum scandens climbing by means of its 

 tendril-like petioles. 



TniGMOTAXis has been observed in some lower organisms {Chlamydomonas 

 Chromatium Weissii) and in some spermatozoids {Fucus). The phenomenon is so 

 rare that its mere mention will be sufficient. 



2. Nastie Movements 



In tlie tropistic and tactic movements of irritability, the direction 

 of the stimulus stands in direct relation to the direction of the move- 

 ment ; the nastie movements on the other hand are either brought 

 about by diffuse stimuli with no definite direction or are not influenced 

 by the direction of the stimulus. The direction of the movement 



