APPENDIX 



419 



centrifugal components, with the result that an S-shaped curvature was formed. 

 Piccard concludes that each part of the root is able to perceive and respond to 

 geotropic stimuli. In this case 

 Czapek's results would be due to 

 the root-apex suppressing or over- 

 coming the stimuli generated in 

 the regions behind. Piccard's cur- 

 vatures might, however, possibly be 

 plastic in origin; and ten experiments 

 failed out of twenty-four tried. 



T>- , , j i r j ,1 . FIG. 70. Diagram showing position of axis of rotation 



JPlCCard alSO found that a rOOt between a a and in regard to >the obliquely-inclined apex 



curved towards a wire kept at high oftheroot - 



potential, and that when root and wire were at still higher but like potentials the root 

 curved away. The first effect is undoubtedly a more or less ' galvanotropic ' one due 

 to the silent discharge from the electrified wire. The other may be of the nature of a 

 ' geotropic ' repulsion or rather of a ' magneto-tropic ' response, produced owing to the 

 varying magnetic permeabilities of the cell-constituents. Piccard supposes that it is 

 due to the direct repulsion acting on the surface-layers, and hence concludes that the 

 'geotropic' irritability is localized in the superficial layers. This assumption is, 

 however, not justified ; and judgement must be suspended until details of the experi- 

 ments are given, or confirmation obtained. The roots were, however, often injured 

 by sparking and ozone. In fact, since leaking is always occurring, and since the root 

 has a high resistance and may undergo polarization, it will always be at a lower 

 potential than the wire when both are attached to the same terminal of the electrical 

 machine. It is also worthy of note that the root and wire were only 3 mm. apart. 



Richter (Zur Frage nach der Function der Wurzelspitze, Wien, 1902 ; Inaug.-Diss. 

 Freiburg) failed to obtain Czapek's results, but F. Darwin (Linn. Soc. Journal Bot., 

 1904, Vol. xxxiv, pp. 266-74) and Massart (Me'm. par 1'Acad. de Belgique, 1902) con- 

 firm Czapek's work by other methods. See also Czapek, Jahrb. f. wiss. Bot., Bd. xxxv. 



Newcombe (Bot. Gazette, 1902, Vol. xxxn,-p. 177) finds that the non-growing 

 zones of roots as well as the apex are sensitive to rheotropic stimuli. 



The Light Position of Leaves. G. Haberlandt (Ber. d. D. bot. Ges., Bd. xxn, 

 1904, p. 105) finds that in various species of Tropaeolum the lamina is able to perceive 

 light stimuli and transmit them to the upper part of the darkened pulvinus ; but the 

 response is slower than normal, and the full position is not always assumed. He 

 concludes that the petiole is responsible for the coarse, and the lamina for the fine 

 adjustment of the leaf. In Begonia discolor the influence of the lamina predominates, 

 and the same applies to Monstera deliciosa, which possesses large pulvini. 



Vochting (Bot. Ztg., 1888) found that on the removal of the laminas of Malva 

 verticillata, the petioles performed no orienting curvatures. 



Krabbe (Jahrb. f. wiss. Bot., Bd. xx, 1889) stated that the leaves of Phaseolus and 

 Fuchsia assumed fixed proper light positions when the lamina was covered with dark 

 paper, but not when the pulvinus was darkened. 



Rothert and Darwin also found that the petiole of Tropaeolum minus was 

 heliotropic, even when the lamina was darkened. 



E e a 



