50 EXPERIMENTAL PLANT PHYSIOLOGY 



large enough, when standing on end, to contain potted 

 plants, are covered with dull black paper both inside 

 and out ; or, better still, the inside only may be papered, 

 while the outside is painted black. Margarine boxes 

 are a convenient size. 



The covers of the boxes are replaced, one by a sheet 

 of blue glass, the other by a sheet of red. 



This is a useful piece of apparatus, and it is therefore 

 worth while to cover the boxes carefully. To keep the 

 sheets of glass in position a beading may be put round 

 the edges of the boxes and the glass fitted into this with 



Fig. 23 



Fig. 24 



small brass catches, or, if preferred, the glass may be 

 put into frames and fitted to the boxes with hinges and 

 a latch. 



A plant depleted of starch is then put into each box, 

 and the boxes are placed so that a good light falls on 

 the coloured screens (Fig. 23). 



For carrying out the experiment by means of 

 coloured solutions, special double bell-jars are prepared 

 (Fig. 24). By means of these double bell-jars the 

 working of the experiment is rendered very simple. 

 The coloured solution is put into the outer jacket of 

 the jar, and underneath the jar is placed a plant whose 

 leaves have been depleted of starch. The whole 

 apparatus is then placed in a good light. 



The blue solution is made oy addmg ammonia to a 

 solution of copper sulphate. At first a precipitate is 



