of Rhythm in Plants. 249 
During the first half-hour the Valerian curved downwards, 
when, at the expiration of this time, the half-turn of the 
spindle occurred, the curvature was immediately reversed. It 
may be well to point out, once and for all, that if the curva- 
ture of the shoot continues unchanged from the end of one 
half-hour to the beginning of the next, that is if it continues 
to curve in its old direction after a half-turn has been made, 
the symbol recording the direction will change. If the shoot 
is curving geotropically upwards and is suddenly rotated on 
its axis through 180°, it will, if it continues the curvature, be 
bending downwards. Similarly in Exp. I, since the two first 
half-hours bear the record Dozvn (or D), it is clear that the 
direction of curvature changed at the turn of the spindle. This 
movement, as well as the temporary downward curve at the 
beginning of the two following periods, is due to the physical 
bending of the shoot, a point in our experiments which 
caused us some difficulty. 
During the last 14' of the third period, a downward 
curvature occurred, and the same movement fills up the last 
2' of the fourth period. These are clearly growth-curvatures 
due to after effect, but not as yet showing any relation to the 
half-hourly period. 
The following experiment shows a similar state of things : — 
Exp. II. May 20, 1889. Valerian. 
p. 
Minutes. 
Movement. 
P 
Minutes. 
Movement. 
I 
16 
? 
! 
D 
14 
D 
V 
0 00 
U 
D 
II 
28 
D 
3 
D 
3 
D 
VI 
8 
U 
III 
i 5 
10 
U 
D 
17 
D 
D 
4 
IV 
25 
U 
VII 
10 
U 
3 
D 
15 
D 
S 2 
