1278 
Botany. — “On the mutual influence of phototropic and geotropic 
reactions in plants.” By Dr. C. E. B. BREMEKAMP. (Communi- 
cated by Prof. F. A. F. C. Went). 
(Communicated in the meeting of March 27, 1915). 
§ 1. Zntroduction. 
It is conceivable that part of the quantity of unilaterally incident 
light which is just sufficient to cause a naked eye curvature in 
etiolated Avena coleoptiles, might be replaceable by a geotropic 
induction of shorter duration than the presentation time. Starting 
from this supposition Mrs. C. J. Rorren— PEKELHARING ') has carried 
out a number of experiments in which the seedling received both a 
light- and a gravitational stimulus, either simultaneously or in rapid 
succession and both lasting about two-thirds of what had been found 
to be the phototropic and the geotropic presentation time. These 
experiments gave uniformly negative results. Macroscopic curvatures 
were never observed. 
Experiments of Mad. PoLowzow’*) and of Matnunrer*) on geotropic 
curvatures and of Arisz*) on phototropic ones, have shown that 
after a stimulus which had no macroscopic effect, deviations from 
the original position could nevertheless be demonstrated with suitable 
apparatus. In this connection the results of Mrs. Rurren’s experiments 
are somewhat puzzling. An obvious deduction from them would be 
that light exercises an unfavourable influence on the gravitational 
reaction or, alternatively, gravity on the phototropic curvature. Before 
abiding by this conelusion, however, it is necessary to take another 
possibility into consideration. 
Statements in the literature show, that in many cases a marked 
difference may be observed between the rates at which the phototropic 
and the geotropie reaction processes proceed. The gravitational cur- 
vature is generally visible sooner and reaches its maximum more 
quickly. When therefore the two stimuli are applied simultaneously 
or immediately after one another, there is every chance that the 
phototropic curvature will only have reached a very small value when 
the geotropic one has already passed its maximum and that, when 
1) GC. J. RurreN—PeKELHARING. Untersuchungen über die Perzeption des Schwer- 
kraftreizes. Recueil des Trav. Botan. Néerl. Vol. VIL 1910. 
2) W. Porowzow. Untersuchungen über Reizerscheinungen bei den Pflanzen. 
Jena 1909. 
3) A. Mattterer. Etude sur la réaction géotropique. Bull. Soc. Vaud. Se. Nat. 
XLVI. 1910. Nouvelle étude experimentale sur le géotropisme. ibidem XLVIIL. 1912. 
4) W.H. Arisz. Proceedings K. Akad. v. Wet. Amsterdam. 1911. 
