210. 
or smaller, but inevitable, observational errors must be added to 
the eecurrence of physical disturbances. 
These considerations have given rise to the planning of an auto- 
graphical method. 
In literature only one apparatus, used for these purposes, occurs; 
namely that of Bose and Das *), who transmit growth on a smoked 
plate, moved on by clockwork, by means of a lever-system at a 
magnification of 1000 to 10000 times. This crescograph can only 
record growth for a very short time, but the authors are not con- 
cerned with this factor, as the growth is so highly magnified. That 
observation-time is, however, of great importance may follow from 
the fact that the changes in velocity of growth, caused e.g. by light, 
are extended over a very long region of time. Further the test-plant 
is fixed on the elaborate lever-system by means of a thread, whereby 
the chance of physical disturbances is enlarged. 
Moreover, this apparatus too is not adapted for use on the clinostat. 
So another kind of auxanometer was constructed in order to evade 
the errors mentioned above. 
The principle of the apparatus. The growing test-plant closes a 
very weak electric circuit, by means of a refined contact, mounted 
on a micrometer-screw. This screw has a pitch of 0,5 m.M.; at its 
end is fixed a cogwheel with 100 teeth. The weak current, closed 
by the plant goes through a relais of high sensibility, which closes 
a stronger circuit. This stronger current moves on the cogwheel 
one, two or more teeth by means of an electro-magnet. 
The screw is turned in this way */,,,, '/,,‚, etc. around its axis, 
the contact thus is raised resp. 5, 10 or more u. The plant has to 
grow 5, 10 or more u before it closes the circuit again. 
Meanwhile a recording-pen on a rolling carriage-frame is moved 
on with a velocity of 1 m.M. a second by an electric clockwork 
(connected with a second-pendulum) along a non-moving recording- 
drum. The pen thus writes a straight line. At the instant of contact- 
making by the plant, the pen leaps back and arriving on its’starting- 
point the drum is turned over a distance of 1,5 m.M. and directly 
the pen begins to write again with the same velocity. In this manner 
a series of lines will arise, while the length of each of them, 
measured in m.M. gives the time, in seconds, needed by the plant 
for growing 5, 10 or more u. The curve, connecting the tops of 
these lines reproduces the course of growth. The machine records 
‘) Sir J. C. Bose and G. Das. Proc. of the Royal Soc. of London, Series B, 
Vol. XC, 1919. nt 
