Prodtiction of Rhythm in Plants. 
99 
P sx 
p vm 
p VII 
observed, which continued after the klinostat was stopped. 
In two experiments this (the c unstimulated rhythm ’) showed 
two reversals of direction. We 
give a single example : — 
Exp. II, Fig. 12 . Valerian, i-hr, 
period. (Geotropism.) Fig. 12 will 
sufficiently explain the results with- 
out giving the full notes. 
There are several curious points 
about this experiment. The change 
in direction of curvature takes place 
not in the middle of the periods (as 
in Fig. 11) but at the horizontal 
lines, that is, the beginning of each 
fresh period. Thus during each 
period the shoot was curving down- 
wards 1 . It is impossible to say 
whether this is due to ‘ sagging/ 
i. e. to the weight of the shoot 
causing it to bend downwards as 
any flexible body would bend, or 
whether it is a true geotropic cur- 
vature which happens to coincide 
with the turning-point of the klino- 
stat. The fact that it occurs in PH! 
Period I makes it probable that it 
is a case of sagging. But the sequel 
of the experiment makes it clear 
that the alternation of stimulus 
was producing an effect. It is there- 
fore probable that the physical 
drooping of the shoot concealed 
any geotropic curves as long as the 
klinostat was in action. The klinostat was stopped in the 
middle of Period IX ; nevertheless, as the thick line shows, 
1 It must be understood that Fig. 1 2 is an abstract of the observations, only the 
critical points of the curve being given. The same is true of Figs. 13 and 14. 
H 2 
P V 
p iv 
p II 
Fig. 12. 
