56 IVaight.—On the Presentation Time and Latent Time for 
to keep the temperature constant, readings were taken morning and even¬ 
ing on a maximum and minimum thermometer. Readings of the relative 
humidity, which could be kept fairly constant at 80-90 per cent., were also 
recorded daily. 
For stimulation the fronds were placed horizontally on their sides, and 
adaxially to the incident light. 1 In order to see if any movement had 
occurred, the outline of the frond was traced on glass, almost in contact with 
it, unless this was impracticable on account of epinastic curvature, when the 
frond was placed against a scale and its position read as exactly as possible 
through a pin-hole. At the end of the period of stimulation, the plant was 
either rotated on the klinostat, or, when this was impossible owing to the 
size or weight of the pot, it was placed so that the frond was quite vertical. 
The following tables, made from actual experiments, typical of a large 
number, show that any difference in the results obtained by the two 
methods is inappreciable: 
Length of 
f?'ond in 
cm. 
Period of 
stimulation 
in hours. 
Angle of Latent time 
curvature • in hours. 
Position of 
plant after 
stimulation. 
7.2 
2 
Stage : Late Lnfant. 
IO° 
6 
On klinostat 
8-5 
2 
10° 
6 
On klinostat 
6.5 
2 
0 
0 
6 
Upright 
io -6 
3 
4 
Stage : Adolescent 3 . 
0 
5 
-1 
5 2 
On klinostat 
20-0 
3 
4 
_o 
7 
. 1 
0 2 
Upright 
10-0 
3 
4 
7 
. 1 
r>2 
Upright 
12-0 
3 
4 
Stage : Adolescent 4 . 
IO° 
5 
5 
On klinostat 
12.5 
3 
4 
10° 
Upright 
When 
upwards of four hundred experiments had 
been carried out in 
this way, an approximate idea was gained of the presentation time at the 
various stages above mentioned. Several critical experiments for each 
stage were then made when the temperature was as nearly as possible 20° C. 
(never above 21 0 C. or below I9°C.). The angle recorded was in every 
case the maximum reached, and the results of these experiments were 
checked by those where no curvature took place with the same or some¬ 
what lower periods of stimulation. This is important, as exposures much 
in excess of the presentation time often produce movements of little or no 
greater amplitude. 
Column 1 in the tables shows that considerable difference in the 
length of the frond does not affect the presentation time and latent time. 
It has been found that these periods depend on the stage y and only indirectly 
on the age or length of the frond. 
1 M he reasons for this position have already been given. Prankerd: loc. cit., p. 145 . 
