On the artificial Production of Rhythm 
in Plants. 
With a note on the position of maximum 
heliotropic stimulation. 
BY 
FRANCIS DARWIN and DOROTHEA F. M. PERTZ 1 . 
With four Figures in the Text. 
I N the Annals of Botany, October, 1892 (Vol. VI, p. 245), 
we described a series of experiments on this subject. We 
remarked (p. 259) that ( Those who repeat our experiments 
must not expect uniform success, as there is undoubtedly 
a certain capriciousness in the results, which probably 
depends on varying degrees of vigour in the plants used. 1 
The present research was begun in the hope of discovering 
a cause for this capriciousness ; in this we have been 
disappointed, nevertheless some of our results seem worth 
printing. 
The fundamental experiment consists in subjecting seedlings 
or growing shoots to a series of opposite stimuli following 
each other at equal intervals of time. The stimuli may be 
either due to gravitation or to light ; in either case they tend 
to produce curvatures in two opposite directions. It might 
1 A note on our results was read before the Cambridge Phil. Soc. on January 
22, 1900. 
[Annals of Botany, Vol. XVII. No. LX V. January, 1903.] 
