182 



EXPERIMENTS WITH PLANTS 



Does this starch come from the supply stored up in 

 the seed-leaves, or is it manufactured in the foliage-leaf? 



Keep a plant in darkness ^ until the 

 leaves no longer give a starch test, 

 then cut off several leaves and place 

 them in tumblers of water; place 

 one -half the number in sunlight and 

 the other half in darkness; take 

 care that the stalk (but not the 

 blade) of the leaf dips under the 

 water (Fig. 101). In two or three 

 days test the leaves which have 

 been in the light. Do you find any 

 starch ? This starch 

 must have been made 

 hy the leaves after they 

 were removed from the 

 'plant. Now test those which have been 

 in darkness. Is the difference due to the 

 absence of light? We may put this to a 

 final test in a very simple way. Pin corks 

 to the opposite sides of a leaf, as shown 

 in Fig. 102, so as to completely exclude 

 light from the covered portion; over an- 

 other leaf put tin-foil so as to cover both 

 sides, having first cut out letters or figures 

 from the tin -foil on the upper surface; 



101. Leaf of English Ivy 

 deprived of starch and 

 placed in water, to see if 

 it can make starch when 

 separated from the plant. 



102. Arrange- 

 ment for ex- 

 cluding . light 

 from a part of 

 the leaf. 



' The plant may be covered with a box or a cone made of pasteboard. 



