N’ewcombe, Gravitation sensiviteness not confined to apex of root. 101 
fuge method as introduced by KnightO and employed by tbe 
two Authors just cited presented itself as tbe obvious way to 
make tbe test. 
It was soon discovered by a searcb of tbe literature tbat 
IViesnei’O bat made precisely tbis test. He bad cut off one or 
two millimeters of tbe root-tips of Zea mais, Pisum sativum, Pha- 
seoliis midtiflorus, and Vicia faha, bad revolyed tbem at a velocity 
ranging fi’om 20 g to 41 g, tberoots being placed at rigbt angies 
to tbe radii of revolution, and bad obtained outward curves in all 
bis bebeaded roots. In sonie cases curves came in roots from 
wbicb 3 mm bad been removed. Wiesner, as we bebeve now. 
beld an erroneous conception of tbe nature of tbe response; but 
be sbould bave tbe credit of carrying out tbe experiment. 
About tbe time tbat AViesner’s work appeared Brunebor st s) 
publisbed an account of a few experiments made witb decapitated 
roots of Pliaseolus on tbe centrifuge revolving at 25 g. Tbis 
Autbor fiUed tbe ebamber boiding bis roots witb moist sawdust 
to prevent tbe plastic bending of tbe roots, and tberewitb obtained 
no emwes tbo bis roots made some growtb. 
Brunebor st used only one species of seedbng in tbe foregoing 
experiment, excised apparently one to two millimeters of tbe root 
tip, and speaks of tbe tendency of tbe sawdust to dry out; yet on 
tbis small sbowins-. Krabbe and otbers at tbe time discredited 
Wiesner’s results, claiming tbat tbe latter’s cuiwes on tbe cen¬ 
trifuge were merely plastic. Czapek, in bis extensive study of 
tbe geotropic sensitiveness of tbe root, pays no attention to tbe 
centrifuge experiments of Wiesner, tbo tbe latter bad offered good 
evidence tbat bis curves were not plastic. Tbis evidence was fur- 
nisbed by setting uninjured seedlings, like tbose decapitated, in a 
damp-ebamber filled witb carbon dioxide, and tben revolving tbe 
preparation so as to give to tbe roots tbe same gravitation acce- 
leration tbat bad produced curves in tbe decapitated roots- In 
such a preparation tbere was not only no growtb, but also no 
ciuwing. Unless one will Claim tbat we may get a plastic bend 
in a gTowing root, tbo none in a non-growing living root, tbe re- 
sult of Wiesner’s is decisive, and it is remarkable tbat none of 
Wiesner’s opponents bas repeated tbe experiment. Czapek^), 
in bis experimeuts employing tbe centrifuge to increase tbe gTa- 
vitation Stimulus, assumes tbat a speed equal to 40 g will not 
cause plastic curving in root-tips; but it was witb a speed no 
gTeater tban tbis and sometimes only baff as great, tbat Wiesner 
obtained bis curves in decapitated roots. Evidently Wiesner’s 
results sbould bave been taken more into account in determining 
tbe extent of tbe geotropicaUy sensitive region in roots. 
0 Philos. Trans. I. 1806. 99. 
2) Untersuchungen über die Wachstumsbewegungen der Wurzeln. (Sitzb. 
K. Akad. Wissensch. Abt. I. LXXXIX. 1884. 223.) 
0 Die Funktion der Spitze bei den Richtungsbewegungen der Wurzeln. 
(Ber. d. d. bot. Gesellsch. II. 1884. 78.) 
Jahrb. wiss, Botanik. XXVII. 1895. 305. 
