TRANSPIRATION 



197 



into one end of the tube. See that the other end is completely full of water 

 and then insert into it a cork with a bent tube {6). Some of the water will be 

 forced along the tube to a point (»), which should be marked with gummed 

 paper. Arrange the apparatus so that the tube i is horizontal and expose 



to a, bright light : the 

 transpiration from the 

 leaves of the shoot soon 

 causes a withdrawal of 

 water along the tube. 



It is necessary that the 

 joints of the apparatus 

 should be air-tight and 

 no bubbles of air should 

 remain in the tube («). 



Ex. 114.— The differ- 

 ence in the transpiration 

 from the two surfaces of 

 a leaf possessing a great 

 many more stomata on 

 F'<=- 86. one side than on the other 



may be shown by placing the leaf between paper which has been steeped in 

 cobalt chloride solution and dried. 



Make a 3 per cent, solution of cobalt chloride and soak some pieces of 

 blotting-paper or circular filter papers in it. Allow the latter to dry in the 

 air. When damp, the cobalt chloride on the paper is pink, but after drying 

 before a hot fire so as to drive off the small remaining amount of water, it 

 becomes bright blue : on' absorbing a slight amount of water from the air or 

 from other sources it becomes pink again. 



Place a leaf of a scarlet-runner between two blue dry pieces of cobalt 

 chloride paper, and ptit the whole between two sheets of glass to prevent 

 absorption of water from the air. After a quarter of an hour, examine the 

 papers and note whether that in contact with the lower or the upper side of 

 the leaf is pinkest. 



Repeat the experiment with leaves of lilac, elder, pear, poplar, plum and 

 other plants. 



Ex. 115. — To show the influence of a covering of cork in preventing loss of 

 water by transpiration, take two potatoes as near the same size as possible. 

 Peel one of them and weigh both separately : leave them exposed to the air 

 for two hours and weigh again to determine which has lost most water. 



Show in the same manner that when the cuticle of an apple is removed, 

 a much more rapid loss of water takes place than when the cuticle is 

 present. 



