LITERATURE 403 



as well as sensitive. Many cryptogams show negative geo- 

 tropism. Many branches and rhizomes show transverse geotro- 

 pism. Among animals, hydroids show negative geotropism. 

 A marked after-effect follows negative stimulation, by means 

 of it we can show that stretching or the geotropic curvature 

 are independent of any control from the tip after once the 

 stimulus has been transmitted to the stretching region. Like 

 other responses to stimuli, geotropism does not occur in the 

 absence of oxygen. 



LITERATURE 



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 IESIELSKI, T. '72. (See Chapter XIV, Literature.) 

 DARWIN, C. '80. (See Chapter XII, Literature.) 

 DARWIN, F. '82. On the Connection between Geotropism and Growth. 



Jour. Linn. Soc. XIX, 218-230. 

 DRIESCH, H. '92. Kritische Erorterungen neuerer Beitrage zur theoretischen 



Morphologic. II. Zur Heteromorphose der Hydroidpolypen. Biol. 



Centralb. XII, 545-556. 1 Oct. 1892. 

 ELFVING, F. '80. Beitrag zur Kenntniss der physiologischen Einwirkung 



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 '80 a . Ueber einige horizontal wachsende Rhizome. Arb. Bot. Inst. Wiirz- 



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account for the Descent of the Radicles in the Germination of Seeds 



shewn by Experiments. Edinb. New Philos. Jour. April, 1829. 



312-317. 

 KIRCHNER, O. '82. Ueber die Empfindlichkeit der Wurzelspitze fur die 



Einwirkung der Schwerkraft. Prog, zur 64. Jahresfeier d. k. Wiirt- 



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