TRANSPIRATION. 211 



Slightly moisten a handful of salt by adding a drop or two 

 of water, sprinkle some of the salt over the upper surface 

 of the leaf and also over the glass side, cover the dish, 

 and note that the salt on the leaf soon becomes deliques- 

 cent, attracting water out of the leaf tissue through the 

 cuticle, while the salt on the slide remains comparatively 

 dry in both cases, of course, the salt absorbs some water 

 also from the air. Instead of salt we may use dry calcium 

 chloride, which readily deliquesces ; or dry cobalt nitrate, 

 which on being dried (e.g. by heating) is blue, but turns 

 red when moist ; or copper sulphate, which is white when 

 dried but blue when moist. 



(6) Take four similar Begonia or Ficus leaves. Make 

 an easily melted mixture of wax and olive oil, and with 

 this cover the upper side of A, the lower side of B, both 

 sides of C, leaving D untouched. In each case fasten 

 a wire or thread, 10 cm. long, into the stalk of the leaf, 

 forming a loop ; smear the cut end of the stalk. When 

 the wax has cooled and set, weigh the four leaves, hang 

 them up, and after some hours of exposure to light weigh 

 them again, and compare the loss in each case. 



(c) Cobalt Paper Method. Soak pieces of filter- 

 paper, or thin white blotting-paper, in 5 per cent, solution 

 of cobalt nitrate (or chloride), and dry them, when the 

 papers turn blue, Take two of the dry cobalt papers, two 

 dry sheets of glass, and a leaf (wiped dry with a soft 

 cloth, if necessary), and arrange them thus : G-lass, 

 paper, leaf, paper, glass. Sheets of mica are perhaps 

 better than glass. Fasten the whole together with clips, 

 and note which surface of the leaf causes the paper to 

 redden or even turn white (owing to transpiration) the 

 more rapidly. Various leaves should be tried, especially 

 those in which the stomata are all or mostly on the lower 

 surface e.g. Ivy, Willow, Phaseolus, Lilac. Test the 

 sensitiveness of the papers to moisture by breathing on a 

 dry paper, and seeing whether it changes from blue to 

 red or faint pink, or nearly white. 



Prepare a number of cobalt papers for further experi- 

 ments ; if put aside, they will probably lose their blue 



