962 APPENDIX. BOOK III. 



Page 768. On the action of electrical currents on growing roots, see Elfving, Ueb. 

 eine Wirkung des galvanischen Stromes auf wachsende Wurzeln, Bot. Zeitg., 1882. 



He finds that when a root is placed vertically between two electrodes, it curves 

 towards the positive electrode ; the curvature is evidently connected with the growth of 

 the root, the current effecting a retardation. Continued exposure to the action of the 

 current causes death. 



When the current is parallel to the long axis of the root it appears to retard growth 

 when it runs in opposition to the direction of growth. 



Experiments with negatively heliotropic roots {Brassica oleracea^ Lepidium sativuniy 

 Sinapis alba), the direction of the current being transverse, showed that they curved 

 towards the negative electrode. 



Page 769. For further researches on DioncBa, see Burdon-Sanderson, On the Elec- 

 tromotive Properties of the leaf oi Dionsea, Phil. Trans. 1882. 



Page 787. Turgidity does not necessarily cause an elongation of cells ; it may also 

 cause them to become shorter and thicker. See de Vries, Ueb. Verkiirzung pflanzlicher 

 Zellen durch Aufnahme von Wasser, Bot. Zeitg., 1879. 



Page 812. Light has some influence on the development of root-hairs on the 

 gemmae of Marchantia ; see Zimmermann, Ueb. die Einwirkung des Lichtes auf den 

 Marchantienthallus, Arb. d. bot. Inst, in Wiirzburg, II, 1882. 



Page 815. On the growth in length of stems, see further, Wiesner, Die undulirende 

 Nutation der Internodien, Sitzber. d. k. k. Akad. d. Wiss. in Wien, LXXVII, 1878. 



Page 839. Geotropism. See F. Darwin, On the Connexion betvi^een Geotropism 

 and Growth, Journ. Linn. Soc, vol. XIX, 1882. 



Page 854, note 2, Further, F. Darwin, On the power possessed by leaves of 

 placing themselves at right angles to the direction of incident light, Journ. Linn. Soc, 

 XVIII, 1881. 



Page 862. On Climbing Plants, see Schwendener, Ueb. das Winden der Schling- 

 pflanzen, Monatsber. d. Bed. Akad., 1881 ; Sachs, Notiz iiber Schlingpflanzen, Arb. d. bot. 

 Inst, in Wiirzburg, II, 1882. 



Page 865. See de Vries, Over de Bewegingen der Ranken van Sicyos, Amsterdam, 

 1880. 



Treub has recently drawn attention to a new group of climbing plants, those namely 

 which climb by means of irritable hooks, the effect of irritation being an increase in the 

 thickness of the hook. Such are Uncaria (Rubiaceae), Ancistrocladus (Dipterocarpeae), 

 Artabotrys (Anonaceae), Lwvunga (Aurantiaceae), Olax (Olacineae), Hugonia (Linaceae), 

 Strychnos (Loganiaceae). This group is not to be confounded with Darwin's * hook- 

 climbers,' the hooks of which are not irritable. (Treub, Sur une nouvelle categoric de 

 plantes grimpantes, Ann. du Jardin botanique de Buitenzorg, III, 1882.) 



Page 871, Sect. 26. Vochting, Die Bewegungen der Bliithen und Friichte, Bonn, 

 1882. 



Page 920, Sect. 35. For some interesting observations as to the relation between 

 plants and external conditions, made on the Flora of Scandinavia, see Bonnier et Flahault, 

 Observations sur les Modifications des V6getaux suivant les conditions physiques du milieu, 

 Ann. Sci. Nat. ser. 6, t. VII, 1879, and Flahault, ibid. t. IX, 1880. 



