14 INJURIOUS TEMPERATURES. [CH. I 



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 well 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. The colour begins to change at about 52° C. 



(13) Temperature. 



If the Oxalis leaf is previously injected wdth water 

 under the air-j)ump, it changes colour at a temperature 

 several degrees lower than in exp. 12. This is a simple way 

 of demonstrating the fact given by Sachs (Physiologie, 

 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- 

 perature of the water more quickly than those of the 

 uniujected leaf, and this is probably the explanation of the 

 difference. 



^ See Chapter iii., on the general conditions of plant life, in Sachs' 

 Text-Book of Botany, Edition ii., also his Physiologie (French Trans- 

 lation), p. 56. 



