260 LIFE MOVEMENTS IN PLANTS 



starta the balancing movement of the plant downwards. On 

 a^ccount of partial balance the record will be found to be 

 less steep than before ; the spead of the clock is gradually 



Fig. 95. — Balanced Creacographic record: (a) sh nving effect oi underbalaiic 

 and (6) overbalance of about 3 per cent. (Magnification 2,000 times.) 



increased till the record becomes perfectly horizontal under 

 exact balance. Overbalance makes the record slope down- 

 wards. In figure 95 is seen records of underbalance (a) 

 and overbalance {b), to the extent of about 3 per cent. 



It will thus be seen that the effect of an external agent 

 may be detected by the upsetting of the balance ; an up- 

 movement indicates (unless stated to the contrary) an 

 enhancement of the rate of growth above the normal ; and 

 a down-movement, on the other hand, a depression of the 

 normal rate. 



Calibration. — The cahbration* of the instrument is 

 obtained in two different ways. The rate of subsidence of 

 the plant-holder, by which the balance is obtained, is 

 strictly proportional to the rate of rotation of the vertical 

 spindle and the attached train of clock-wheels. A striker 

 is attached to one of the wheels, and a bell is struck 

 at each complete revolution. The clockwork is adjusted 



