GEOTROPISM. II 445 



DUTROCHET. 1824. Recherches sur la structure intime etc. 



ELFVING. 1884. Ofversigt finska Wetensk. forhandlingar. 



[FITTING. 1905. Jahrb. f. wiss. Bot. 41, 221 and 331.] 



FRANK. 1868. Beitr. z. Pflanzenphysiologie. Leipzig. 



HABERLANDT. 1900. Ber. d. bot. Gesell. 18, 261. 



HABERLANDT. 1902. Ibid. 20, 189. 



HABERLANDT. 1903. Jahrb. f. wiss. Bot. 38, 447. 



[HABERLANDT. 1905. Ibid. 42, 321.] 



HOFMEISTER. 1863. Jahrb. f. wiss. Bot. 3, 77. 



JOHNSON. 1828. Comp. Linnaea, 1830, ,5, 145, Abstract of literature. 



JOST. 1901. Bot. Ztg. 59, i. 



JOST. 1902. Biolog. Centrbl. 22, 161. 



KARSTEN. 1890. Ber. d. bot. Gesell. 8 (55). 



KNIGHT. 1806. Ostwald's Klassiker, Nr. 62. Leipzig, 1895. 



KOHL. 1894. Die Mechanik der Reizkrummungen. Marburg. 



[LUXBURG. 1905. Jahrb. f. wiss. Bot. 41, 399.] 



[MASSART. 1902. Mem. couron. in 8vo, Acad. Bruxelles.] 



MEISCHKE. 1899. Jahrb. f. wiss. Bot. 33, 337 (363, note i). 



MOISESCU. 1905. Ber. d. bot. Gesell. 23, 364. 



NEMEC. 1900. Ber. d. bot. Gesell. 18, 241. 



NEMEC. 1901. Jahrb. f. wiss. Bot. 36, 80. 



[N^MEC. 1905. Studien iiber Regeneration, p. 334. Berlin.] 



NOLL. 1888. Arbeit, bot. Instit. Wurzburg, 3, 496. 



NOLL. 1892. Ueber heterogene Induktion. Leipzig. 



NOLL. 1 896. Das Sinnesleben d. Pflanzen. Ber. Senkenberg. Gesell. Frankfurt. 



NOLL. 1900. Jahrb. f. wiss. Bot. 34, 457. 



NOLL. 1902. Ber. d. bot. Gesell. 20, 403. 



[NOLL. 1905. Sitzungsb. d. niederrhein. Gesell. Bonn.] 



PFEFFER. 1875. Periodische Bewegungen. Leipzig. 



PFEFFER. 1 893 a. Die Reizbarkeit der Pflanzen ( Verhandl. Gesell. d. Naturforscher). 



PFEFFER. 1893 b. Druck- und Arbeitsleistung (Abh. Kgl. Gesell. Leipzig, 20). 



[PICCARD. 1904. Jahrb. f. wiss. Bot. 40, 94.] 



PINOT. 1829. Annal. Sc. nat., I re Ser. 17, 94. 



[RiCHTER. 1902. Function d. Wurzelspitze. Diss. Freiburg.] 



SACHS. 1872. Arbeit, bot. Instit. Wurzburg, i, 193. 



SACHS. 1873 a. Flora, 56, 321. 



SACHS. 1873 b. Arbeit, bot. Instit. Wurzburg, i, 385. 



SACHS. 1874. Ibid, i, 584. 



SACHS. 1879. Ibid. 2, 209. 



SACHS. 1888. Ibid. 3. Plates. 



SCHOBER. 1899. Anschauungen iib. den Geotropismus seit Knight. Hamburg. 



DE VRIES. 1880. Landw. Jahrbucher. 



LECTURE XXXV 

 GEOTROPISM. II 



HITHERTO we have confined ourselves exclusively to a study of those 

 parts of the plant, such as the chief root or chief shoot, whose position of equi- 

 librium is at right angles to the earth's surface, and which bend back again 

 by growth movements into that position if they be placed in any other. We 

 may describe such organs as orthotropic, distinguishing in them two varieties of 

 geotropism, negative and positive. A casual glance at plants as a whole teaches 

 us, however, that there are many plant organs whose position of equilibrium 

 is other than vertical, and these we term plagiotropic, including under that 

 name oblique directions of growth as well as horizontal. It is possible for 

 an orthotropic organ to become plagiotropic under the influence of two forces, 

 i.e. gravity and some other directive force, much in the same way as a body 

 under the influence of two forces acting in different directions obeys neither 

 but takes a new direction easily calculated by reference to the law of the 



