186 



EXPSlilMEN'rS WITH PLANTS 



becomes greatly modified so as to be like that of foli- 

 age-leaves. At the same time they acquire a green 

 color and begin to manufacture 

 starch. 



This principle is so general that 

 we are justified in looking for similar 

 structures wherever similar functions 

 occur. 



Of what is starch made? We may 

 get some indication of this by decom- 

 posing starch by means of heat in 

 the apparatus shown in Fig. 105. If 

 a test-tube is not obtainable, use any 

 piece of glass tubing (the thinner it 

 is the less liable it is to crack) 

 sealed at one end. Place the starch 

 in it and heat slowly. When the starch begins to 

 turn brown, water will col- 

 lect on the sides of the 

 tube ; this also takes place 

 if we dry the starch to con- 

 stant weight, at the tem- 

 perature at which water 

 boils, before beginning the 

 experiment . The water 

 must, therefore, result from 

 the decomposition of the 

 starch. If we conduct the 



104. A seedling of Castor- 

 bean, showing how the 

 seed - leaves assume the 

 form and function of 

 foliage-leaves. 



105. Apparatus for the decompositlou of 



starch: the gases pass into a tumbler 

 of lime-water. 



