92 



PLANTS MAKE FOOD 



parts of leaves covered with vaseline will be found to contain no 

 starch, while parts of the leaf without vaseline, but exposed to the 

 sun and air, do contain starch. 



Air is necessary for the proems of starch making in a leaf, 

 not only because carbon dioxide gas is absorbed (there are from 

 three to four parts in ten thousand present in the atmosphere), 



Diagram to show starch making. Read the text carefully and then explain 



this diagram. 



but also because the leaf is alive and must have oxygen in order to 

 do work. This oxygen it takes from the air around it. 



Comparison of Starch Making and Milling. The manufacture 



of starch by the green leaf 

 is not easily understood. 

 The process has been com- 

 pared to the milling of 

 grain. In this case the 

 mill is the green part of the 

 leaf. The sun furnishes the 

 motive power, the chloro- 

 plasts constitute the ma- 

 chinery, and soil water and 

 carbon dioxide are the raw 

 products taken into the 

 mill. The manufactured 

 product is starch, 1 and a 

 certain by-product (corre- 

 sponding to the waste in a 



Diagram to illustrate the formation of mil1 ) is als g iven ut ' This 



starch in a leaf. by-product is oxygen. To 



1 Sugar is first manufactured and then transformed into starch. 



