CH. l] INJURIOUS TEMPERATURES. 15 



(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 (Beta) may be used in this way as a rough 

 indicator of the temperature at which the protoplasm is 

 killed. Cut a slice of beet-root, 3 or 4 mm. in thickness, 

 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, but the temperature should be allowed to 

 rise very slowly. A temperature of 55 or even 57 will 

 be required. 



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 l . 



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 (6) are reserved for comparison. The dry seeds 

 (b) 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' Physiologic (French Tr.), p. 72. Fig. 8. 



