20 4 



TROPIC MOVEMENTS 



ones, causing tropic curvatures often directed towards the replacement of 

 the missing organs. 



If the apex of Picea excelsa or of other Coniferae is embedded in a plaster cast, 

 one or more of the side-shoots bend upwards and more or less completely replace the 

 main axis 1 . Char a behaves similarly -, while in many other plants a certain lessen- 

 ing in the geotropic angle of the side-shoots is produced by the removal of the apical 

 shoot 3 . According to Strasburger 4 , the effect extends to lateral shoots of Picea 

 pungens grafted upon the main axis of Picea excelsa when the apex of the latter is 

 embedded in a plaster cast. Similar changes of position may be produced by the 

 infection of the axis with parasitic fungi 5 . In many cases, however, in which sympo- 

 dial axes are normally produced by the non-development of the terminal bud, the 

 required directive actions probably result from self-regulation rather than from any 

 modification of the geotropic irritability 6 . On the other hand, the upward curvature 

 of the previously horizontal apex of a rhizome to form an annual upright shoot seems to 

 result from a change of the original diageotropic irritability into a negatively geotropic 

 one, and this change is correlated with the conversion into a leafy and flowering 

 shoot 7 . A change of the geotropic irritability not only occurs in sympodial rhizomes, 

 but also in uniaxial ones, and is produced or hastened by the removal or bending of 

 the subaerial shoots 8 . No such change is, however, produced in the rhizome of 

 Adoxa moschatellina by the removal of the flowering axes 9 . 



The removal of the apex of the main root also causes the lateral roots to grow 

 more directly downwards, owing to a change in their geotropic tone, without their 

 reaching a vertical position 10 . Vochting n found that, when the apical portion of the 

 tap-root of a beet was transplanted into the position of a lateral root, it grew in 

 a plagiotropic position, whereas a lateral root transplanted into the cut end of the 

 main root assumed a positively parallelotropic position. Apparently the irritabilities 

 were reversed in these cases by the correlative influence of the new associations. 

 Nemec 12 also found that the removal of the terminal leaflet of a compound leaf 

 influenced the position of the lateral leaflets to a certain extent. 



1 Kunze, Flora, 1851, p. 145 ; Sachs, Arb. d. bot. Inst. in Wiirzburg, 1879, Bd. II, p. 280; 

 Busse, Flora, 1893, p. 144. 



3 Richter, Flora, 1894, p. 416. 



3 Vochting, Organbildung, 1884, Bd. n, p. 32. 



4 Jahrb. f. wiss. Bot., 1901, Bd. xxxvi, p. 588. 



5 Darwin, The Power of Movement in Plants. 



6 Cf. Goebel, Vergl. Entwickelungsgesch. d. Pflanzenorgane, 1883, p. 192. 

 Cf. Goebel, 1. c., p. 193 ; Organography, Vol. n, 1905, p. 25. 



* Cf. Goebel, Bot. Ztg., 1880, p. SiS ; Organography, Vol. I, 1900, p. 172 ; Vol. II, 1905, p. 4^3 

 (Spargamum, Sagittaria, Circaea, Scirpus maritinnts, &c.) ; Sachs, Arb. d. bot. Inst. in Wurzburg, 

 1880, Bd. n, p. 484 (Cordyline, Yucca} ; Elfving, ibid., 1880, Bd. II, p. 489 ; C. Kraus, Flora, 1880, 

 p. 54; Vochting, Bot. Ztg., 1895, p. 95 (Potato). 



9 Goebel, Bot. Ztg., 1880, p. 791. 



10 Sachs, Arb. d. bot. Inst. in Wurzburg, 1874, Bd - ! . P- 622 5 Darwin, The Power of Movement 

 in Plants, 1880, p. 187; Vochting, Organbildung, 1884, Bd.ll, p. 35; Boirivant, Ann. sci. nat., 1898, 

 7" sen, T. vi, p. 315. 



1 Vochting, Transplantationen am Pflanzenkorper, 1892, p. 34. 



1 N6mec, Ueber die Folgen d. Symmetriestbrung bei zusammengesetzten Blattern, 1902 (reprint 

 from Bull, internal, de 1'Acad. de Boheme). 



