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 



20-23 



17 



14 



12 



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 



