Balls . — Temperature and Growth 561 
Before a new chamber is used it is soaked in warm water for two days 
in order to remove any soluble bodies from the sealing-wax which cements 
the cover-slip and from the thin rubber band. 
Application of heat. The preliminary experiments referred to above 
were made in a Pfeiffer Hot-Box. I found, when the thermo-electric method 
of temperature measurement was adopted, that the temperature of the 
object on the cover-slip usually lagged behind that indicated by the 
thermometer in the air of the box by as much as 5 0 C. when the rate of 
heating was rapid. Since the temperature of the object could now be 
determined accurately without employing the cumbersome box, the latter 
was abandoned in favour of the following plan for applying the heat directly 
to the microscope stage. 
Qq 
