CH. l] INJURIOUS TEMPERATURES. 11 



perature of the water more quickly than those of the 

 uninj acted leaf, and this is probably the explanation of tha 

 difference. 



(14) Temperature. 



When a turgid cell is killed the cell sap escapes 

 through the dead protoplasmic wall, and if the cell sap is 

 coloured, the escape will be a marked occurrence. The 

 Beet-root may be used in this way as a rough indicator 

 of the fatal temperature at which the protoplasm is 

 killed. Cut a slice of beet-root, wash it to free it from 

 any cell sap adhering to the cut surfaces, and suspend it 

 with a thermometer in a beaker of water at about 25° C, 

 which is to be heated as in experiment 12. 



A similar experiment may be more accurately made 

 under the microscope, using one of the methods described 

 below, by which a microscopic object can be subjected to a 

 given temperature. 



(15) Dry and soaked seeds^. 



The effect of a high temperature depends, among other 

 things, on the condition of the subject of the experiment. 

 Thus, dry seeds can endure a temperature which is fatal 

 to seeds which have been soaked. 



Take 20 peas, half of which (a) are to be left in water 

 for 12 hours, or until they are thoroughly soaked, while 

 the other 10 (b) are reserved for comparison. The dry seeds 

 (6) are placed in a dry test-tube, while the imbibed seeds 

 (a) are placed in a test-tube half full of water: both 



1 Sachs' Physiologie (French Tr.), p. 72. Fig. 8. 



