34 CELL-CONTENTS AND CELL-WALLS. 



brown. The pressure has destroyed the protoplasm and 

 made it permeable to the acid sap, which then decomposes 

 the chlorophyll. 



(/) Another indication of the death temperature of 

 protoplasm is afforded by cells with coloured sap, e.g. 

 those of Beetroot. We have already noted that when 

 Beetroot sections are heated the red sap escapes from the 

 cells. Cut a thin slice (3 or 4 mm.), rinse it in cold water 

 (to remove any sap on cut surfaces), and suspend it, with 

 a thermometer, in a beaker of cold water ; then gradually 

 heat the water. The red sap does not, as a rule, escape 

 until the temperature exceeds 55 C. 



(g) Here is another proof of the difference between living 

 and dead protoplasm as regards permeability. Cut two 

 fairly thick slices of Beetroot and rinse them thoroughly 

 in water. Place one slice in some cold water in a beaker 

 (A). Plunge the other slice in boiling water to kill it, 

 and then place it in water in a second beaker (B). After 

 an hour take some water from each beaker ; add in each 

 case a few drops of sulphuric acid and boil, then pour in 

 some Fehling's solution and boil again. Sugar is present 

 in the water in B, but not in A. 



(h) Cut out two pieces of fresh Turnip, rinse them in 

 water; kill one piece by immersion in very hot water. 

 Mince a piece of Beetroot, boil with water, and pour the 

 red juice into a shallow dish, and lay in the juice the two 

 pieces of turnip. Note that, after a day's immersion, the 

 killed piece of turnip is stained right through, while the 

 living piece is unstained or only slightly stained on the 

 surface. 



(i) Cut a fairly thick (about 1 cm.) slice of Beetroot, 

 rinse it in water, wipe it dry, and place it in a glass jar 

 with a cork, through which passes a thermometer. Put 

 the jar in a larger vessel containing a freezing mixture of 

 snow (or broken ice) and salt, giving a temperature of 

 6C. or lower. After a time quickly remove and 

 examine the frozen slice ; its surface is covered with a 

 layer of ice, consisting of parallel rods, most abundant on 

 the lower side where the slice was in contact with the 



