the carbon dioxid absorbed froin the air 

 with some of the "water brought up by the 

 roots. The process by zvhich these com- 

 pounds a7'e united is a co^nplex one, but 

 the ultimate result is starch. — The snow 

 on black soil melts quickly because the 

 black absorbs the heat of the sun. The 

 green chlorophyll of the leaf absorbs cer- 

 tain heat rays, and this heat affords a 

 peculiar vital energy which enables the 

 living matter of the leaf to unite 

 carbon dioxid and water. No one knows 

 all the details of this process ; and our 

 first definite knowledge of the product 



I. Excluding light from begins when starch is deposited in the 



a part of a leaf. . 



leaves. 



Starch is composed of carbon, hydrogen and oxygen (C^H^^Oj). 

 The sugars and the woody substances are very similar to it in 

 composition. All these substances are called carboh3^drates. 



In making this starch from the carbon and oxygen of carbon 

 dioxid and from the hydrogen and ox)^gen of the water, there is 

 a surplus of oxygen. It is this oxygen 

 which is given off into the air. 



The process of using the carbon dixoid 

 of the air is known as carbon assimilation. 



8. Starch is present i7i the green leaves 

 of plants which have been exposed to sun- 

 light ; but in the dark 7io starch can be 

 formed from carbon dioxid. — Procure at 

 the drug store an ounce or so of tincture 

 of iodine. Pour a drop or two of this 

 iodine on some ordinary starch paste or 

 a slice of potato. The starch is colored 

 blue or purplish-brown. This reaction is 

 characteristic of starch. Now pour some 

 of the iodine on the leaf from which we 

 dissolved the chlorophyll in a previous 

 experiment (page 3). Note that the leaf 

 is colored purplish-brown throughout. The leaf contains starch. 



2. The effect on the leaf. 



