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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 satinjum^ 
Sinapis alba), the direction of the current being transverse, showed that they curved 
towards the negative electrode. 
Page 769. For further researches on Dion(Ea, see Burdon- Sanderson, On the Elec- 
tromotive Properties of the leaf of Dionsna, 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. Verkürzung 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 
Marchantienthalius, Arb. d. bot. Inst, in Würzburg, 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 between 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. Berl. Akad., 188 1 ; Sachs, Notiz über Schlingpflanzen, Arb. d. bot, 
Inst, in Würzburg, 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. Vöchting, Die Bewegungen der Blüthen und Früchte, 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 V^g^taux suivant les conditions physiques du milieu, 
Ann. Sei. Nat. ser. 6, t. VII, 1879, and Flahault, ibid. t. IX, 1880. 
