238 BOTANICAL GAZETTE [MARCH 
Geotropism.—GROTTIAN?? finds that by the use of proper concentrations of 
amyl alcohol and other anesthetics it is possible to stop geotropic response in 
horizontally placed roots without entirely stopping growth. He believes he has 
shown that anesthetics may abrogate the power of perception without entirely 
eliminating the power of reaction. He finds that certain.concentrations of the 
et accelerate growth, as has been shown by several other investigators. 
ds likewise much evidence, though not entirely conclusive, that concen- 
ae which greatly stimulate growth also shorten reaction time. 
he same author has repeated all of CzAPEK’s experiments on the change of 
metabolism due to geotropic stimulation. As is well known, CzAPEK claims that 
geotropically stimulated root tips show a greater percentage of homogentisic 
acid than unstimulated ones, and that.the accumulation is due to the ae 
of an antienzyme which stops the action of the enzyme which carries on the fu 
metabolism of the acid. Several authors have already shown that paps: s 
method of detecting the acid are not at all reliable, and even that neither tyrosin 
from which the acid is derived nor the ‘acid itself is present in the root (geotropi- 
cally stimulated or not) in detectible quantities. GrortiAn finds that even 
stimulated and unstimulated roots. It seems then that CzaPEk’s methods do not 
indicate any change in the metabolic products due to geotropic saeese/2i much 
less the accumulation of homogentisic acid. —WILLIAM CROCKE 
In x BLaauw determined that in stimulation by tight ae presentation 
time is veh proportional to the intensity of the light used. The suggestion 
that the same would be found true with the effective force in stimulation by 
gravitational and centrifugal acceleration has been tested by Miss C. J. PEKEL- 
NG, who reports? that she has established this relation for the same plant 
under identical conditions with continuous stimulation. This completes the 
proof that with both sorts of stimuli and with both continuous and intermittent 
application, the product of the presentation time and the force of the stimulus 
isaconstant. The validity of WeBER’s law for geotropic curvatures is questioned, 
and FirriNc’s experiments on this point are considered inconclusive. By tes 
the action of gravity and light together, it appeared that the mode of perception 
of the two is not the same. There was not the least evidence that positive of 
negative reaction to gravity could be obtained by increasing or decreasing the 
strength of the stimulus. One of the most striking results of the investigation has 
been emphasized by WENT (under whose direction it was conducted) in a separate 
22 GROTTIAN, WALTER, sete zur Kenntniss des Geotropism. Beih. Bot. 
Centralbl. 24: ale og. 
23 PEKEL , CATHARINA J., Onderzoekingen over die perceptie van = 
evaarckachiprkel door planten. Proefschrift ter verkrijging van der graad . 
ie plant- en dierkunde, aan de Rijks-Universiteit te Utrecht. 8vo. pp. 195- pls. 4- 
1909 
