64 



PLANT GROWTH AND NUTRITION 



ground, straightens out. From between the cotyledons the bud- 

 hke plumule or epicotyl grows upward, forming the first true 

 leaves and all of the stem above the cotyledons. As growth con- 

 tinues, we notice that the cotyledons become smaller and smaller, 

 until their food contents are completely absorbed into the young 

 plant. The young plant is now able to care for itself and may 

 be said to have passed through the stages of germination. 



What makes an Engine Go. — If we examine the sawdust or 

 soil in which the seeds are growing, we find it forced up by the 

 growing seed. Evidently work was done; in other words, energy 

 was released by the seeds. A familiar example of release of 

 energy is seen in an engine. Coal is placed in the firebox and 

 lighted, the lower door of the furnace is then opened so as to make 

 a draft of air which will reach the coal. You know the result. 

 The coal burns, heat is given off, causing the water in the boiler 



to make steam, the engine wheels to turn, 

 and work to be done. Let us see what 

 happens from the chemical standpoint. 



Coal, Organic Matter. — Coal is made 

 largely from dead plants, long since pressed 

 into its present hard form. It contains a 

 large amount of a chemical element called 

 carbon, the presence of which is character- 

 istic of all organic material. 



Oxidation, its Results. — When things con- 

 taining carbon are lighted, they burn. If we 

 place a lighted candle which contains carbon 

 in a closed glass jar, the candle soon goes out. 



The limewater test. The ^\ ^e then Carefully test the air in the jar 

 tube at the right shows with a substance known as limewater,^ the 

 dioxide.^ ° ^ ^^^ °^ latter, when shaken up with the air in the 



jar, turns milky. This test proves the pres- 

 ence in the jar of a gas, known as carbon dioxide. This gas is 

 formed by the carbon of the candle uniting with the oxygen in 



1 Limewater can be made by shaking up a piece of quicklime the size of your 

 fist in about two quarts of water. Filter or strain the limewater into bottles and 

 it is ready for use. 



