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, 

 w^ash 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 allow^ed to 

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

 be required. 



A similar experiment may be more accuratel}^ 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 (6) are reserved for comparison. The dry seeds 

 {h) are placed in a dry test-tube, w^hile the imbibed seeds 

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



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



