TYPICAL TENDRILS. 66l 



pletely emerged from the bud state, and have reached about three-fourtlis of their 

 definitive size ; in this condition they are extended straight, and the apex of the 

 shoot which bears them usually makes revolving nutations. The tendril itself 

 also exhibits the same phenomenon, becoming curved along its whole length 

 (usually with the exception of the rigid basal portion and the hooked apex), in 

 such a manner that the upper side, the right, the lower, and the left side become 

 convex in turn; no torsions make their appearance. During this revolving nutation 

 the tendril is rapidly growing in length and is irritable to contact ; i. e. every 

 more or less pronounced touch on the irritable side effects a concave curvature 

 at the spot touched, and this curvature then extends further up and down. If 

 the contact is transitory, the tendril subsequently straightens out again. The 

 degree of irritability^ is very different according to the species: in Passiflora 

 gracilis a pressure of one milligram sufirces to effect the curvature in a short time 

 (25 seconds) ; with others a pressure of 3 or 4 milligrams is necessary, and the curva- 

 ture occupies a longer time (after 30 seconds with Sicyos\ The tendrils of other 

 species become curved within a few minutes after being rubbed slightly at one spot ; 

 in Dicenlra thalictrifolia after half an hour, in Smilax not till after more than an hour; 

 in Ampehpsis still more slowly. The curvature on the touched side increases for 

 some time, then stops, and then after some time (often several hours) the tendril 

 again becomes straightened, in which condition it is again irritable. Tendrils the 

 apices of which are slightly incurved are only irritable on the concave lower side ; 



1 The following publications treat of both tendril-plants and twining-plants : — 



Hugo Mohl : ' Über den Bau und das IVittden der Ranken und Schlingenpflanzen,' Tübingen, 

 1827. 



Charles Darwin : 'The Movements and Hahits of Climbing Plants,' London, 1875. 



On the irritability and movements of tendrils the following may be consulted : — 



Hugo de Vries: ^ Längenwachst hum der Ober- und Unterseite sich kiünimendcr Ranken^ 

 Arb. d. bot. Inst, in Wzbg., B. I, p. 302. 



* Über die inneren Vorgänge bei doi Wachsthuniskrilmmungen mehrzellige Organe^ Bot. Zeitg., 

 1879, p. 830. 



Casimir de Candolle : ' Ol'servatioiis sur fenroulonent des Vrilles,' Bibliotheque universelle 

 de Geneve, Jan., 1877, T. LVIII. 



Treub describes (Anji. dujardin botanique de Buitcnzorg, vol. iii, pp. 1-87, Leiden, 1882) a new 

 class of climbing plants, the climbing organs of which are in effect very short, curved, hook-like 

 tendrils, which on contact with a support grow in thickness to an unusual extent. 



On twining plants the following may be consulted : — 



Hugo de Vries : ' Zur Mechanik der Bewegung von Schlingpflanzen,' Arb. d. bot. Inst, zu 

 Würzbg., B. I, 1874, p. 317. 



Schwendener: ' Über das Winden der Pflanzen,' Monatsher. der Berliner Akad., Dec, iSSi. 



In Opposition to the latter treatise, which depends on very scanty observations, I wrote a note 

 {^ A'otiz über Schlingpflanzen') in Arb. d. bot. Inst, zu Wzbg., B. II, p. 719. 



Schwendener's reply to this note (Jahrb. f. wiss. Bot., B. XIII, II. 2") leaves no doubt that he 

 was entirely iinacquainted with the most important phenomena described in the present lecture, and 

 in my note referred to, whence his reply is completely without object. I believe that in this 

 lecture that, without setting up any theory, I have indicated the path along which the true cause of 

 twining is to be found ; in the case of phenomena so involved it is above all important to test the 

 scientific weight of the individual observations, and little is won by making a few obserwitions on 

 one or several plants and seeking to give to these a particularly important look by means of mathe- 

 tical formula. 



