PLANTS MAKE FOOD 



91 



ceived from the sun, manufacture starch out of certain raw materials. 

 These raAv materials are soil water, which is passed up through 

 the bundles of tubes into the veins of the leaf from the roots, and 

 carbon dioxide, which is taken in through the stomata or pores, 

 which clot the under surface of the leaf. A plant with variegated 

 leaves, as the coleus, makes starch only in the green part of the 

 loaf, even though these raw materials reach all parts of the leaf. 



Light and Air necessary for 

 Starch Making.- - If we pin strips 

 of black cloth, such as alpaca, over 

 some of the leaves of a growing 

 hydrangea which has previously 

 been placed in a dark room for a 



An experiment to show the effect of ex- 

 cluding light (but not air) from the 

 leaves of a green plant. The result of 

 this experiment is seen in the next 

 picture. (Experiment performed by 

 C. Dobbins and A. Schwartz.) 



Starchltss area in a leaf caused 

 by excluding sunlight by 

 means of a strip of black 

 cloth. 



few hours, and then put the plant in direct sunlight for an hour 

 or two, we are ready to test for starch. We then remove some of 

 the covered leaves and extract the chlorophyll with wood alcohol 

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

 color of the starch test). A test then shows that starch is present 

 only in the portions of the leaves exposed to sunlight. From this 

 experiment we infer that the sun has something to do with starch 

 making in a leaf. The necessity of a part of the air (carbon 

 dioxide) for starch making may also easily be proved, for the 



