Kewcombe, Gravitation sensiviteness not confined to apex of root. 101 



fuge method as introduced by K night 1 ) and employed by the 

 two Authors just cited presented itself as the obvious way to 

 make the test. 



It was soon discovered by a search of the literature that 

 Wiesner 2 ) hat made precisely this test. He had cut off one or 

 two millimeters of the root-tips of Zea mais, Pisum sativum, Pha- 

 seolus multiflorus, and Vicia faba, had revolved them at a velocity 

 ranging froni 20 g to 41 g, theroots being placed at right angles 

 to the radii of revolution, and had obtained outward curves in all 

 his beheaded roots. In some cases curves came in roots froin 

 which 3 mm had been removed. Wiesner, as we believe now. 

 held an erroneous conception of the nature of the response; but 

 he should have the credit of carrying out the experiment. 



About the time that Wiesner's work appeared Brunchorst 3 ) 

 published an account of a few experiments made with decapitated 

 roots of Phaseollis on the centrifuge revolving at 25 g. This 

 Author filled the Chamber holding his roots with moist sawdust 

 to prevent the plastic bending of the roots, and therewith obtained 

 no curves tho his roots made some growth. 



Brunchorst used only one species of seedling in the foregoing 

 experiment, excised apparently one to two millimeters of the root 

 tip, and speaks of the tendency of the sawdust to dry out; yet on 

 this small showing, Krabbe and others at the time discredited 

 Wiesner's results, claiming that the latter's curves on the cen- 

 trifuge were merely plastic. Czapek, in his extensive study of 

 the geotropic sensitiveness of the root, pays no attention to the 

 centrifuge experiments of Wiesner, tho the latter had offered good 

 evidence that his curves were not plastic. This evidence was fur- 

 nished by setting uninjured seedlings, like those decapitated, in a 

 damp-chamber filled with carbon dioxide, and then revolving the 

 preparation so as to give to the roots the same gravitation acce- 

 leration that had produced curves in the decapitated roots. In 

 such a preparation there was not only no growth, but also no 

 curving. Unless one will Claim that we may get a plastic bend 

 in a growing root, tho none in a non-growing living root, the re- 

 sult of Wiesner's is decisive, and it is remarkable that none of 

 Wiesner's opponents has repeated the experiment. Czapek 4 ), 

 in his experiments employing the centrifuge to increase the gra- 

 vitation Stimulus, assumes that a speed equal to 40 g will not 

 cause plastic curving in root-tips; but it was with a speed no 

 greater than this and sometimes only half as great, that Wiesner 

 obtained his curves in decapitated roots. Evidently Wiesner's 

 results should have been taken more into account in determining 

 the extent of the geotropically sensitive region in roots. 



!) Philos. Trans. I. 1806. 99. 



2 ) Untersuchungen über die Wachstumsbewegungen der Wurzeln. (Sitzb. 

 K. Akad. Wissensch. Abt. I. LXXXIX. 1884. 223.) 



3 ) Die Funktion der Spitze bei den Richtungsbewegungen der Wurzeln. 

 (Ber. d. d. bot. Gesellsch. II. 1884. 78.) 



4 ) Jahrb. wiss. Botanik. XXVII. 1895. 305. 



