Centrifugal Force as Geo tropic Stimuli. 733 
R — average number of rotations per sec. whilst running 
62,654-47,772 
= = 4-69. 
4,034 p 
•*- R 2 = 1 3' 2 ♦ 
Now in this experiment the point of equilibrium was 1 cm. below the middle of 
the box, and at this point the radius of rotation = 19 cm., i. e. r — 19. 
Cent, force = tt 2 R 2 r = 39-5 x 13-2 x 19 
= 10,222 dynes 
10,222 
= 10-42 mg. 
But since gravity was also working the whole time we should take the value of the 
resultant of gravity and the centrifugal force in the direction 6° below the horizontal. 
This — C — (10-42 cos 6°+ 1 sin 6°) mg. 
= (10-42 X 0-99454- 0-1045) mg. 
— 10-46 mg. 1 
In this experiment the value of the mechanical error correction, i. e. M.E.C. = 0-93. 
C t 
C (corrected) = 10-46 x 0-93 = 9-7 mg. .*. — - = 9-7, but 10. 
C. T 
— °-97 5 which is an approximation to 1. 
Experiments. 
Helianthus animus. The * seeds ’ of Helianthus were soaked in water for 
twenty-four hours in a dish, which in winter was placed on the hot-water pipes. 
They were then sown upright in damp sand and kept at a temperature of 
about 20° C. They were ready for experimenting from forty-eight to seventy- 
two hours after the commencement of soaking. In general the radicles were 
2 to 10 mm. long at the beginning of an experiment. In all about 135 ex- 
periments have been carried out on the radicles of Helianthus annuus ; but 
of these the first fifty have been disregarded, as in the light of later experi- 
ence it was seen that sufficient precautions had not been taken in these 
earlier experiments to avoid errors. They served the purpose of providing 
experience in the use of the centrifugal machine, but will not be employed 
in deducing results. In many others the line of equilibrium did not fall 
within the limits of the box, so that the radicles either bent all upwards or 
all downwards. From these it can only be shown that with the times 
taken ( t and T) the centrifugal force necessary just to neutralize gravity is 
either less or greater than the calculable amount. If it had been possible 
to predict at the beginning of the experiment the centrifugal force that 
would be obtained sufficiently closely, failures arising from this source 
1 When the centrifugal force is high this correction makes very little difference and can be 
neglected. 
