IOI 
Production of Rhythm in Plants. 
universal ; see for instance, Annals of Botany, VI, pp. 357- 9, 
where in Exps. X and XI the reversal of the curve, in light 
experiments on Phalaris , occurs in the middle of the periods. 
To return to Fig. 13, the klinostat was stopped in Period 5 
and the plant arranged so that no fresh heliotropic stimula- 
tion could occur in the original plane. The thick line shows 
two reversals of curvature occurring at approximately the 
right times. 
Exp. IV, Fig. 14, December 
1, 1899. Oat seedling. Half- 
hourly period. (Heliotropism.) 
We give this experiment in 
order to make it clear that 
there is no necessary connexion 
between heliotropism and the 
quarter-hourly period, and that 
a plant can equally well acquire 
a half-hourly rhythm by alter- 
nate light-stimuli. 
It should be noted that in 
Fig. 14 the curvature of the 
seedling, as soon as it becomes 
regular in Period 5, is away 
from the light, not towards the 
light as in Fig. 13 ; we are 
unable to explain the difference 
between the two cases. The 
klinostat was stopped in Period 
9, and the thick line shows two 
reversals at approximately half 
an hour’s interval, the first ti 
This is another good instance c 
1 being somewhat belated, 
‘unstimulated rhythm.’ 
Alternate Unequal Stimuli. 
We made a good many heliotropic experiments with 
alternating but uitequal periods of illumination, in the hopes 
of building up an unequal rhythm. The intermittent 
