3i8 NATURE-STUDY 



To show that light is necessary for starch formation, and 

 that the chlorophyll alone is not sufficient, place a geranium 

 or nasturtium in a dark room or in a hght-tight box for a day 

 or so. Then test as before and no starch will be found in 

 the leaves. 



These experiments show that starch is formed in the green 

 parts of plants, and in the presence of sunhght. This shows 

 the great importance of sunlight to plants. Why do we 

 place house-plants in the window? Plants like geraniums 

 placed in dark or shady places would be in a starving con- 

 dition. Explain. 



The leaf absorbs carbonic acid gas from the air, and water 

 is brought to it from the root. Out of these substances the 

 leaf cells make the starch. The leaf, therefore, is a very 

 important organ to the plant. The explanation of starch 

 formation as it takes place in the leaf need not be given in 

 the grades. Let it be sufficient to show that the leaf does 

 make starch. A figurative explanation may, however, be 

 given in this manner: "The leaf is a mill where the raw 

 materials taken in by the plant are ground and prepared. 

 The raw materials are water and carbon dioxide. The 

 millstones are the chlorophyll grains, and the power that 

 turns them is the sunhght." The figure is very apt. 



The starch is used by the plant as food, and is readily 

 converted into sugar, and vice versa. Thus we have the 

 sugar in sugar cane and fruit. By the addition of the mineral 

 salts (nitrates, potash, hme salts, phosphates, etc.) taken in 

 by the roots, other food substances (proteids) are made by 

 the plant. 



Sometimes the food is not all used up immediately by the 

 plant but is stored for a time as a reserve. Thus we find 



