FUNCTIONS OF LEAVES 169 



A very good comparison of the leaf to a mill has been 

 made as follows 1 : 



The mill : Palisade-cells and underlying 



cells of the leaf. 



Raw material used : Carbon dioxide, water. 



Milling apparatus : Chlorophyll grains. 

 Energy by which the mill 



is run : Sunlight. 



Manufactured product : Starch. 



Waste product : Oxygen. 



180. Plants Destitute of Chlorophyll not Starch-Makers. 

 Aside from the fact that newly formed starch grains are 



first found in the chlorophyll bodies of the leaf and the 

 green layer of the bark, one of the best evidences of 

 the intimate relation of chlorophyll to starch-making is 

 derived from the fact that plants which contain no chloro- 

 phyll cannot make starch from water and carbon dioxide. 

 Parasites, like the dodder, which are nearly destitute of 

 green coloring matter, cannot do this; neither can sapro- 

 phytes or plants which live on decaying or fermenting 

 organic matter, animal or vegetable. Most saprophytes, 

 like the moulds, toadstools, and yeast, are flowerless plants 

 of low organization, but there are a few (such as the 

 Indian pipe (Plate V), which flourishes on rotten wood 

 or among decaying leaves) that bear flowers and seeds. 



181. Detection of Starch in Leaves. Starch may be 

 found in abundance by microscopical examination of the 

 green parts of growing leaves, or its presence may be 

 shown by testing the whole leaf with iodine solution. 



1 By Professor George L. Goodale. 



