10 INJURIOUS TEMPERATURES. [CH. I 



control a similar eudiometer is fitted up with non-succu- 

 lents, such as pieces of young sunflower^ 



Section B, The effect of various temperatures : 

 of certain poisons : and of electrical shock. 



(12) Temperature. 



To get a rough idea of the upper limit of temperature 

 which ordinary plants can endure, it is best to make a few 

 simple experiments with plants in which the moment of 

 death is marked by some obvious change, e.g. in colour. 

 Oxalis acetosella is useful for this purpose, because death 

 is indicated by a dingy yellow colour due to the action 

 of the acid cell-sap on the chlorophyll. 



Fill a beaker with water at 25° C, and suspend in it 

 a thermometer, to the bulb of which a leaf of Oxalis is 

 attached. Heat the water by means of a gas flame, and 

 note the temperature at which the leaf loses its fresh 

 green tint. 



(13) Temperature. 



If the Oxalis leaf is injected with water before the experi- 

 ment, it changes colour at a temperature several degrees 

 lower than in (12). This is a simple way of demonstrating 

 the fact given by Sachs (Physiologie Veg6tale, p. 71) 

 that plants in air endure a temperature which they cannot 

 bear in water. 



The cells of the injected Oxalis leaf acquire the tem- 



1 To complete the experiment, the relative acidity of the Eochea ia 

 the evening and next morning, should be compared. See Part n. 



