160 



GROWTH. 



[CH. VI 



bud. Place the pot on a layer of damp sand at the 

 bottom of a galvanised iron cylinder so supported that a 

 flame can be placed under it when it is desired to expose 

 the plant to a higher temperature. The manipulation 

 necessary in starting the experiment will probably in- 

 terfere with the growth of the scape, so that it should be 

 allowed to grow for 3 or 4 hours without further disturb- 

 'ance. A spirit-lamp or very small gas-flame is then 

 lighted under the cylinder, and the temperature of the air 



14' 



17° 



20-23' 



Fig. 30. Exp. 186. 



within the cylinder carefully watched for some little time. 

 After 2 or 3 hours during which, if the temperature has 

 been raised by some 10°, the steps traced on the drum 

 will greatly increase in vertical height, — the flame is 

 extinguished so that the fall in rate of growth may be 

 recorded. Fig. 30 gives a copy of a tracing taken as here 



