8o 



BOTANY. 



Starch formation, by- 

 green plants. 



Synopsis. 



Carbon dioxide is absorbed by the green parts of 



plants. 

 In the presence of chlorophyll in the cell, and under 

 the influence of sunlight, a. chemical change takes 

 place in the carbonic acid (carbon dioxide united 

 with the water in the plant-cell). 

 As a result of this chemical change starch is formed 

 by the union of carbon, hydrogen, and oxygen ; 

 but all of the oxygen brought in by the carbon 

 dioxide is not needed in the manufacture of starch. 

 This portion of the oxygen is set free. 

 Fungi, or other plants which lack chlorophyll cannot form starch. 

 Parts of leaves, or parts of plants, which lack chlorophyll cannot form 

 starch. 



Chlorophyll is the green pigment in the chlorophyll bodies (chloroplasts). 

 Starch is first formed in the chlorophyll bodies, and then dissolved and 

 carried to other parts of the plant, for food, or to be stored. 



Material. — Fresh leaves of ordinary plants which have been for a few 

 hours in daylight (some of the seedlings which have been grown, or plants 

 from the greenhouse will answer); some variegated leaves of the coleus 

 plant if possible. 



For study of chlorophyll, leaves of begonia to section are good. For 

 study of starch, potato tubers ; and if other objects are wanted, sweet pota- 

 toes, onions, etc. 



If the pupils make their own sections of the begonia leaves, sharp razors 

 will be necessary. 



Chemicals needed in the test for starch : a solution of iodine in potassium 

 iodide (see appendix for formula), or an ordinary tincture of iodine ob- 

 tained at drugstores ; alcohol. 



Microscope, etc., if it is desired to demonstrate the structure of starch 

 grain. 



