1896] LABORATORY APPARATUS IN VEGETABLE PHYSIOLOGY 467 
force acts in a plane at right angles to that of gravity, and the 
direction of growth is a resultant of the two forces; when the 
disk is whirled vertically gravitation is neutralized. In order to 
secure these positions the first machines made, which were 
exhibited? at the 
same time as_ the 
auxanometer already 
mentioned, had the 
moist chambers sup- 
ported on a metal 
arc, and held in place 
by a set screw in the 
base (~/. XXV). But 
it was found difficult 
to accurately center 
the pulley wheel for 
the different posi- 
tions, and later ma- 
chines have been 
made with the cham- 
ber Supported on a 
Pinion (fig. 7). 
When the electric 
Motor is used it is 
mounted, along with 
the chamber, on a 
Wooden base (p/. XXV); when other motive power is employed 
the chamber is mounted on a heavy iron base (fig. 7). To 
‘Scertain the speed of the disk a piece of paper is passed over a 
revolving pencil point for an exact number of seconds. The pencil 
Point is attached eccentrically to the lower end of the spindle 
“trying the cork disk (pl. XXV) and describes a spiral as the 
Paper is moved over it. By counting the number of turns of the 
ae the number of revolutions of the disk for the time is 
nd, 
Fic. 1. Centrituge with iron base. 
3 Ibid, 344. 
