STARCH MADE BY A GREEN LEAF 81 



Starch made by a Green Leaf. — Remember that the upper 

 surface of the leaf is placed toward the sun and that the leaf must 

 be thought of as a solar engine. 



If we examine the palisade layer of the leaf, we find cells which 

 are almost cylindrical in form. In the protoplasm of these cells 

 are found a number of tiny green 

 bodies, the chloroplasts or chlo- ^^^^-^ X^ 



rophyll bodies . If the leaf is placed 

 in wood alcohol, we find that the 

 bodies still remain, but that the 

 color is extracted, going into the , 

 alcohol and giving to it a beautiful 

 green color. The chloroplasts are, 

 indeed, simply part of the proto- 

 plasm of the cell colored green. 



rrn IT r xi X J. Variegated leaves of tradescantia. 



Ihese bodies are oi the greatest 



importance directly to plants and indirectly to animals. The 

 chloroplasts, by means of the energy received from the sun, manu- 

 facture sugars and starches out of certain raw materials obtained from 

 the soil and the air. These raw materials are soil water, which is 

 passed up from the roots through the bundles of tubes into the 

 veins of the leaf, and carbon dioxide, which is taken in through 

 the stomata or pores. A plant with variegated leaves, as the 

 tradescantia or " wandering Jew," makes starch only in the 

 green part of the leaf, though these raw materials reach all parts 

 of the leaf. 



The change of color of leaves in autumn seems to be due to 

 loss of chlorophyll, plus the formation of a red pigment in the cells. 

 It is probably not frost that causes leaves to turn but rather a 

 combination of lower temperature with other factors. 



Light and Air Necessary for Starch Making. — If we pin strips 

 of black cloth, such as alpaca, over portions of several leaves of a 

 gi-owing hydrangea which has previously been placed in a dark 

 room for a few hours, and then put the plant in direct sunlight for 

 an hour or two, we are ready to test the leaves for starch. We 

 remove the partly covered leaves, boil them to stop further 

 changes, and extract the chlorophyll with wood alcohol (because 

 the green color of the chlorophyll interferes with the blue color of 



